I have a pair of 1960 vintage PPK's (a .22LR and a .32 Auto) and a P-38 in .22LR. I have spare firing pins for the .22LR PPK and P-38, and plenty of magazines for all three. What other replacement parts should I try to keep on hand?
Depends on how many rounds you actually plan on putting down range. Most PPK's are safe queens or get little use, hence why older guns can still be purchased in very good condition.
Things that I have seen wear out from extreme use are the trigger bar, hammer (specifically the tooth portion), and cocking piece, but we are talking LOTS of rounds. And then there's the many springs. Keeping things clean will go a long way in preserving the internals. My guess is that the most commonly replaced part would most likely be the loaded chamber indicator spring.