Where can I find legendary crafting materials?

This Diablo 3 Craftables Spreadsheet is particularly helpful when trying to figure out if you are in an area with a possible legendary crafting material drop.

Here is the same list in not so sortable form:

Legendary Crafting Materials:

• Adventurer's Journal
  • Found in: Acts 1-4 - Various World Objects
  • Used For: Pender's Purchase
• Angelic Shard
  • Found in:
    • Act 4 - The Great Span: Izaul
    • Act 4 - Multiple Areas: Corrupted Angel
    • Act 4 - The Silver Spire Level 1: Pyres the Damned
    • Act 5 - Pandemonium Fortress Level 2: Celic
  • Used For: Hallowed Protectors Set
• Behistun Rune
  • Found in:
    • Act 1 - Leoric's Manor: Krailen the Wicked
    • Act 2 - Road to Alcarnus: Yeth
  • Used For: Mark of the Magi
• Bloody Pincer
  • Found in:
    • Act 3 - Tower of the Damned Level 2: Crabbs
    • Act 3 - The Core of Arreat: Scorpitox
    • Act 5 - Ruins of Corvus: Balata
  • Used For: Demon Claw
• Born's Key
  • Found in:
    • Act 1 - Cemetary of the Forsaken: Lucious the Depraved
    • Act 1 - Defiled Crypt: Digger O'Dell
    • Act 1 - Defiled Crypt: Dataminer
    • Act 1 - Defiled Crypt: John Gorham
  • Used For: Born's Command Set
• Captured Nightmare
  • Found in:
    • Act 4 - The Silver Spire Level 2: Grimnight the Soulless
    • Act 4 - The Silver Spire Level 1/2: Terror Demons and Enslaved Nightmares
  • Used For: Night's Reaping
• Captured Soul
  • Found in:
    • Act 3 - The Keep Depths Level 2: Aloysius the Ghastly
  • Used For: Lai Yui's Persuader
• Cartographer's Toolkit
  • Found in:
    • Act 1 - Festering Woods: Grimsmack
    • Act 1 - Festering Woods: Enkidu (Ancient War Event)
    • Act 3 - Rakkis Crossing: Lavarinth (Blaze of Glory Event)
    • Act 3 - Tower of the Damned: Gholash
  • Used For: Board Walker's
• Cultist Blood
  • Found in:
    • Act 1 - Halls of Agony: Cultist Grant Inquisitor
    • Act 2 - Alcarnus: High Cultist Murdos
    • Act 2 - Alcarnus: Jhorum the Cleric
  • Used For: Blood Magic Dagger
• Defiled Doll
  • Found in:
    • Act 4 - The Silver Spire Level 1: Kysindra the Wretched
    • Act 5 - House of Deep Sorrow: Lady Victoria (Event Spawn)
  • Used For: Spite
• Demon Skin
  • Found in:
    • Act 3 - The Core of Arreat: Axgore the Cleaver
    • Act 3 - Tower of the Damned Level 1: Haxxor
    • Act 4 - Gardens of Hope Tier 1: Khatun
    • Act 4 - Gardens of Hope Tier 2: Razorclaw
  • Used For: Demon's Hide Set
• Element of Celerity
  • Found in:
    • Act 1 - The Weeping Hollow: Mange
    • Act 1 - Fields of Misery: Burrow Bile (The Forlorn Farm Event)
    • Act 1 - Fields of Misery: Dreadclaw the Leaper
    • Act 1 - The Lost Mine (Fields of Misery): Shanabi (Precious Ores Event)
    • Act 1 - Watch Tower Level 2: Armorer's Bane (Scavenged Scabbard Event) Used For: Fleeting Strap
• Essence of the Twin Seas
  • Found in:
    • Act 2 - Black Canyon Mines: Razormouth
    • Act 2 - Sewers of Caldeum: Moontooth Dreadshark
  • Used For: Captain Crimson's Trimmings Set
• Eternal Power Capsule
  • Found in:
    • Act 1 - Whimsyshire: Evil Oliver
  • Used For: Arcane Barb
• Eyes of the Dead
  • Found in:
    • Act 1 - Leoric's Passage: Headcleaver (Quest Spawn)
    • Act 1 - Cathedral Level 2: Merrium Skullthorn
  • Used For: War of the Dead
• Frozen Blood
  • Found in:
    • Act 3 - Caverns of Frost: Chiltara
  • Used For: Utar's Roar
• Glowing Ore
  • Found in:
    • Act 5 - Battlefields of Eternity: Sartor
    • Act 5 - Pandemonium Fortress: Soul Scavenger (The Souls of Angels Event)
  • Used For: Cosmic Strand
• Griswold's Scribblings
  • Found in:
    • Act 1 - Cathedral: Bookshelves
    • Act 1 - Cemetery of the Forsaken: Gravedigger's Corpse
    • Act 1 - Festering Woods: Enmerkar (Last Stand of the Ancients Event)
    • Act 1 - Wortham Chapel: Bookshelves
    • Act 2 - Khasim Outpost: Cain's Lost Satchel
    • Act 2 - Khasim Outpost: Imperial Guard Supplies
    • Act 2 - Zoltun Kulle Dungeons: Bookshelves
    • Act 3 - Skycrown Battlements: Morgan's Satchel
    • Act 3 - The Keep Depths: Lore Objects
    • Act 4 - Multiple Areas: Angel Archives
  • Used For: Griswold's Perfection
• Hilt of the Silver Wolf
  • Found in:
    • Act 3 - Arreat Crater Level 1: Growlfang
    • Act 3 - Tower of the Damned Level 1: Gnawbone
  • Used For: Golden Scourge
• Human Cartilage
  • Found in:
    • Act 1 - Cathedral Level 2: Cudgelarm
    • Act 1 - Defiled Crypt Level 2: Mangelmaw
  • Used For: Wall of Man
• Iron Wolves Doctrine
  • Found in:
    • Act 2 - Dahlgur Oasis: Ssthrass
  • Used For: Asheara's Vestment Set
• Living Flame
  • Found in:
    • Act 4 - The Silver Spire Level 2: Sao'Thall
    • Act 4 - The Silver Spire Level 2: Rhau'Kye
    • Act 4 - Radiant Chapel: Malfeas the Abhorrent
  • Used For: Cinder Switch
• Lyekurn's Diary
  • Found in:
    • Act 3 - The Heart of Sin: Azmodan
  • Used For: Corruption
• Maghda's Tormented Soul
  • Found in:
    • Act 2 - Lair of the Witch: Maghda
  • Used For: Cain's Destiny Set
• Mystical Source
  • Found in:
    • Act 1: Whimsyshire: Midnight Sparkle
    • Act 1: Whimsyshire: Nightmarity
    • Act 1: Whimsyshire: Team Unicorn
    • Act 1: Whimsyshire: Creampuff
  • Used For: Sage's Journey Set
• Phial of Weakness
  • Found in:
    • Act 3 - The Battlefields: Deadgrasp
    • Act 3 - The Battlefields: Handible (Triage Event)
  • Used For: Atrophy
• Quaking Vial
  • Found in:
    • Act 4 - Hellrift Level 1: Sledge
    • Act 4 - Hellrift Level 2: Hammermash
  • Used For: Sunder
• Reaper's Fear
  • Found in:
    • Act 5 - Heart of the Fortress: Maltheal
  • Used For: Reaper's Wraps
• Rydraelm Tome
  • Found in:
    • Act 2 - The Lost Caravan (Stinging Winds): Beyatt
    • Act 2 - Daulguhr Oasis: Ashangu
  • Used For: Mantle of the Rydraelm
• Shard of the Ensteig Plate
  • Found in:
    • Act 1 - Defiled Crypt: Lord Dunhyld (The Matriarch of Bones Event)
    • Act 1 - Festering Woods: Feklar's Ghost
    • Act 1 - Festering Woods: Hawthorne Gable
    • Act 2 - Sewers of Caldeum: Shade of Nar Gulle
    • Act 2 - Unknown Depths: The Archivist (Event Spawn)
    • Act 2 - Tomb of Khan Dakab: Spirit of Khan Dakab (Event Spawn)
  • Used For: Aughild's Authority Set
• Shattered Core
  • Found in:
    • Act 2 - Forgotten Ruins: Ancient Guardian
    • Act 2 - Unknown Depths: Rockgut
    • Act 2 - Realm of Shadow: Thrum
  • Used For: Devastator
• Shimmering Quill
  • Found in:
    • Act 1 - Dank Cellar: Sarkoth
    • Act 1 - Musty Cellar: Gorathra
    • Act 3 - Keep Depths Level 1: Thornback
  • Used For: Unbound Bolt
• Shuddering Demon Bone
  • Found in:
    • Act 4 - Gardens of Hope Tier 2: Koa' Ahn
    • Act 4 - Gardens of Hope Tier 2: Oah' Tash
  • Used For: Archfiend Arrows
• Skeleton's Dice
  • Found in:
    • Act 4 - Gardens of Hope Tier 1: Torchlighter
    • Act 5 - Battlefields of Eternity: Emikdeva
    • Act 5 - Battlefields of Eternity: Korchoroth
  • Used For: Skeleton's Deceit
• Skull of Raylend
  • Found in:
    • Act 3 - The Keep Depths Level 2: Bholen
    • Act 3 - Rakki's Crossing: Garganug
    • Act 3 - Core of Arreat: Gorog the Bruiser
  • Used For: The Helm of Rule
  • Sydyru Bone
  • Found in:
    • Act 1 - Cathedral Level 1: Gildewing
    • Act 1 - Cathedral Level 1: Firestarter
    • Act 1 - Fields of Misery: Sicklefang (Carrion Farm Event)
    • Act 3 - Unknown Depths: Hellscream
  • Used For: Sydyru Crust
• Symbol of the Guardian Brotherhood
  • Found in:
    • Act 3 - Skycrown Battlements: Thromp the Breaker
    • Act 3 - Stonefort: Bashface the Truncheon
    • Act 3 - Stonefort: Dragus (Waiting for Reinforcements Event)
    • Act 3 - The Keep Depths Level 2: The Crusher
    • Act 3 - Rakkis Crossing: Busaw (Crazy Climber Event)
  • Used For: Guardian's Jeopardy Set
• Torn Soul
  • Found in:
    • Act 1 - Southern Highlands: Lorzak the Powerful
    • Act 1 - Southern Highlands: Skehlinrath
  • Used For: Living Umbral Oath
• Urn of Quickening
  • Found in:
    • Act 2 - Stinging Winds: Erach
    • Act 3 - Caverns of Frost Level 2: Chiltara
    • Act 3 - Caverns of Frost Level 2: Scathach the Savage
    • Act 3 - Icefall Caves: Zelusa the Grasping
    • Act 5 - Heart of the Fortress: Malthael (* May be a bug)
  • Used For: Kethryes' Splint
• White Oak Splinter
  • Found in:
    • Act 1 - Secluded Grove (Fields of Misery): The Old Man
  • Used For: Rozpedin's Force
• Wooden Stake
  • Found in:
    • Act 1 - Cathedral Level 4: Killian Damort
    • Act 3 - The Keep Depths Level 3: Belagg Pierceflesh
  • Used For: Blitzbolter
• Woven Plate
  • Found in:
    • Act 1 - The Cathedral Level 4: Captain Cage
    • Act 1 - The Festering Woods: Enmerkar (The Last Stand of the Ancients Event)
    • Act 3 - The Keep Depths Level 1: Captain Donn Adams
  • Used For: Piro Marella

Infernal Machine Crafting Components:

• Key of Bones
  • Found in:
    • Various Acts - Keywardens
  • Used For:
    • Infernal Machine of Bones
    • Infernal Machine of Evil
    • Infernal Machine of Gluttony
    • Infernal Machine of War
• Key of Evil
  • Found in:
    • Various Acts - Keywardens
  • Used For:
    • Infernal Machine of Bones
    • Infernal Machine of Evil
    • Infernal Machine of Gluttony
    • Infernal Machine of War
• Key of Gluttony
  • Found in:
    • Various Acts - Keywardens
  • Used For:
    • Infernal Machine of Bones
    • Infernal Machine of Evil
    • Infernal Machine of Gluttony
    • Infernal Machine of War
• Key of War
  • Found in:
    • Various Acts - Keywardens
  • Used For:
    • Infernal Machine of Bones
    • Infernal Machine of Evil
    • Infernal Machine of Gluttony
    • Infernal Machine of War

Source for the various locations

According to this page on Diablofans, only Malthael himself drops this specific crafting material:

• Acquired from: Act V, Heart of the Fortress, Malthael
• Where to farm: Act V, Heart of the Fortress
• Used for: Reaper's Wraps, Wrists, Health globes restore 25–30% of your primary resource, 5 random magic properties (as opposed to the 8 properties according to Battle.net)
• Note: Malthael also drops the Recipe for Reaper's Wraps.

This sounds pretty plausible to me as I also got the plan from him (which seems to be a guaranteed drop).