Hello! From what we know, rep parts are not currently sold by factories, so finding a caseback for PAM000 can be a problem, although you can ask your TD if there is such a part from HWF, XF or NOOB of the latest samples, maybe they can be of some help.
Also, you can try to write a DSN (He is not stable in communication and he has little left, but if he has such a part, he will most likely answer you), or contact Jacob on the homage forum, he may make something for you . Otherwise, on eBay or Ali you can look for sterile casebacks for 44mm cases.
Good luck!