No idea, but isn't the PT57 the same size as the PT58? I don't know if the parts are interchangeable, but I'd check in to that. Numrich (no affiliation, although I've been called a numbskull) has quite a few PT58 parts, surprisingly. GunBroker, from time to time, has PT58 "parts kits" that seem to run in the $60's or $70's so if the PT58 is a match, those may be beneficial as well.
Also, wasn't there a PT92c that was a smaller version of the PT92 that was the same frame as the PT57, and PT58? I'm not that well versed on these things, so this may be meaningless ramblings from a, well, numbskull.
Well, it's good to know that the PT57 (at least yours) made it to the USA. I'll keep looking for one and maybe someday, get lucky. I believe they are still produced and sold in other parts of the world where .32 is the largest caliber that subjects can have. Maybe, someday, there will be an importer bring some in.