Where can I get all the warframe parts?

Bosses at the end of each planet. Here's the current list:

http://guidescroll.com/2013/01/warframe-boss-locations-and-drops-list/

Boss: Captain Vor
Planet: Mercury
Level: Tolstoj
Faction: Grineer
Drops: Cronus longsword/Seer Pistol Blueprint Parts

Boss: The Jackal
Planet: Venus
Level: Fossa
Faction: Corpus
Drops: Rhino Warframe Bluprint Parts

Boss: Counceler Van Dek
Planet: Earth
Level: Everest
Faction: Grineer
Drops: Trinity Warframe Bluprint Parts

Boss: Sargent Nef Anyo
Planet: Mars
Level: War
Faction: Grineer
Drop: Mag Warframe Bluprint Parts

.

Boss: The Golem
Planet: Jupiter
Level: Themisto
Faction: Infected
Drops: Volt Warframe Bluprint Parts

Boss: General Sargas Ruk
Planet: Saturn
Level: Thetys
Faction: Grineer
Drop: Ember Warframe Bluprint Parts

Boss: Tyl Regar
Planet: Uranus
Level: Titania
Faction: Grineer
Drop: Ash Warframe Bluprint Parts

Boss: The Hyena
Planet: Neptune
Level: Psamathe
Faction: Corpus
Drops: Loki Warframe Bluprint Parts

Boss: Ambulas
Planet: Pluto
Level: Hades
Faction: Corpus
Drop: Excalibur Warframe Bluprint Parts

.

Boss: Lt. Lech Krill
Planet: Ceres
Level: Exta
Faction: Grineer
Drop: Frost Warframe Bluprint Parts

Boss: Phorid
Planet: Eris
Level: Naeglar
Faction: Infestation
Drop: Nyx Warframe Bluprint Parts

Boss: Kela De Thaym
Planet: Sedna
Level: Merrow
Faction: Grineer
Drop: Saryn Warframe Bluprint Parts

Boss: N/A – Given as Reward at the end of each mission
Planet: Europa
Level: Intel, Captured and Defense Missions
Faction: Infested/Corpus
Drop: Banshee Warframe Blueprint Parts

Boss: Alad V
Planet: Jupiter
Level: Themisto
Faction: Corpus
Drop: Valkyr Warframe Blueprint Parts
Alerts:
+ Dark Sword, Plasma Sword, Jaw Sword, Pangolin Sword, Heat Sword,
+ Heat Dagger, Ceramic Dagger, Dark Dagger, Glave
+ Orikin Catalyst and Reactor
+ Alternative Helmets
+ Orikin Artifact Cards

The best practice if you want to build a Warframe is to go to this Warframe Wikia page and choose which Warframe you want to build.

Then inside every Warframe detail page, you can find who/where you can drop the items needed.

For example in the Ember page it says

Component blueprints drop from General Sargas Ruk (Tethys, Saturn)

I always suggest to visit the wiki because it happened that after an update, all the components for a specific Warframe were dropped by a different boss, or even not dropped at all anymore! The wiki usually mantains those informations as updated as possible.

Also, not every Warframe is dropped by a boss. For example the Vauban components can only be found in Alerts, Mirage components are found during a specific Quest, while Banshee components can be bought inside a Clan Dojo.