For what it's worth, thermoplastic was available years ago (and most likely still is) in sheets for use by orthotists and physical therapists, who used it to make custom-molded splints and braces. I mention this because this product may be more reasonably priced for the health care industry than it is for jewelers (isn't everything?).
It’s reusable. If you have a splint made or a friend does, ask the
therapist for the scraps they cut off as they shape the splint
(especially the non-perforated sections). Reuse the material in the
splint when no longer needed. It also makes a tough, non-marring
surface for forming when molded over an appropriately-shaped wood