There are plenty of secondary markets for eyes- Dreaming Tree Studios is popular with many, and I’ve hear of a couple taxidermy supplies- Tohickon comes to mind. I haven’t painted a flap cat and don’t know the size, but the sticky thread would have it.
I have sanded a damaged Windstone with a small weak dremel, it did great. I imagine hand sanding with a finer grit would work also. However, perhaps the damaged area could be filled in with something like Apoxie-Sculpt without sanding, not seeing the damage?
P.S. it’s gypsum, not plaster, and does act different than plaster or ceramics do.