http://www.airsoftcanada.com/showthread.php?t=166456
A local on the forum here had a Maruzen PPK and did a build. Bit of a long shot but he may possibly have some info to help you. Might be a safer be to also try a larger international forum like arnies as well.
Also this:
http://www.geocities.jp/timmfc2/toyg.../Mznppks1.html
Also, google is saying the PPK is also a umarex licensed product. Not sure if that would help your searches. Though I could be completely wrong about everything here.