Can't find old single handle shower cartridge replacement.

[royce]

I can't find a single handle shower faucet cartridge replacement for a 1972 year mobile home. There is no brand name on the fixture, and only a non-identifiable logo on the handle. Been searching the internet for days - no success. I have pictures but don't know if I can upload them here. I live in a rural area so in-person shopping is difficult.