So I need the monster carapace to finish the Ursine master set. However, I know that I had previously dismantled all of my draconid related hides but I don't have any carapaces. Are there any places to find roaming wyverns/ basalisks etc. in Velen?

SPOILER

... up on the hill above the crones (crookbag bog, or whatever this area is called).

I believe that any "named" carapace can be dismantled into a monster carapace.

indeed i wholeheartedly agree

... point to another one:

to the NE of the crows nest (baron), there is a ruined tower, underneath is a small cave.

- tower: use your witcher senses to find a chest under all the rubble (under charred wood beams). Inside you'll find a recipe that you most certainly will be glad to have.

- cave: this is part of the "shrieker" contract that you will find inside the crows nest >>> you'll be asked to kill a monster that happens to be a wyvern, carapace included :).

Good luck!