Where do I find monster carapace?

Solution 1:

Similar to my answer here, talking about Monster Hide, you can dismantle materials such as Wyvern Hide into Monster Carapace.

According to other sources, you can also purchase it at high level armorsmiths, though I have not seen that.

You can convert these items into monster carapace:

• Basilisk Hide
• Forktail Hide
• Wyvern Hide

Solution 2:

I was looking for monsters to get monster carapace and monster hide needed for upgrades of Witcher Gear. Unfortunately I had already slain all big monsters, done all quests, destroyed all monster nests, etc (OCD anyone?).

But I found this cave I visited before with a bunch of respawned Devourers close to the entrance, a Harpy or 4 furthermore down the cave and 3 Erynia flying monsters at the bottom. On my first visit to this cave I had looted and killed everything, so imagine my joy that all these monsters respawned in between visits.

And - JAY! – I got me 3 Necrophage hides amongst others. You can find the cave next to the fast travel point of Clan fordarroch Forge – Skellige (south-west of Kaer Trolde).