Hey,
this is not a part that you can buy as a service part or part seperately. Its a common problem of these cases to loose it. Most of the guys having problems with missing bezel, let them reproduce by their watchmakers. I would say in the case of the Super Divette, its cheaper to buy one of these NOS Jet/ Super Divette cases at ebay that are floating around from time to time. Pricewise they cost around 250€, which could be cheaper than reproducing in the end.
Nico