Look for an old smith. PPs and PPKs are not hard to get working, they just have some very specific things you have to do to them. Smiths like me that have been around 30-40 yrs will know what to do.
This smith used to work for interarms when they were the Walther importer.
He has an excellent reputation with the Walther's and probably would have no problem with a war-time version..........