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).

Up on the hill? Can you be more specific with cardinal directions perhaps

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!