I know very little about those late model Avanti’s, but I would imagine very few parts specific to the Avanti body were stock piled….. and if a few were stock piled, who is holding them at this point?
Problems such as this can be a real challenge when you own a very limited production car…….
Too bad they made a stressed part like that out of fiberglass or plastic, and I agree replacing it is probably going to be a custom job……. Good luck.