I seem to recall reading about people installing Novak's Colt Mustang sights on PPKs and PPK/Ss.  You'd have to mill off the front sight and use a dovetail cutter then probably fit the rear sight but it doesn't look too hard for anyone with some machining experience.  For some reason I pulled my old Interarms gun out of the safe last night and was thinking about changing the near worthless factory sights; it needs refinishing anyways.  Probably more money than I want to put into a gun I haven't shot in years but figured I'd ask.

M&M can probobly help you or cylinder and slide

@sandboxmedic

Not Novaks per se, but appear to be Trijicons:
http://tooltechgunsight.com/product/walther-ppk-ppks/

Or contact Novak themselves, installation prices seem fairly reasonable (this is in addition to the cost of sights I assume):
https://www.novaksights.com/products.aspx?CAT=9473

Thanks for the links.  I had Novak put sights on a Hi-Power some years ago; I just need to call them and see if they'll do the Walther.  Unfortunately, the PPK has been bumped to the back burner for the foreseeable future, just not enough money to put into a gun I very rarely shoot anymore.