Why not go with an STG76 from BRP? It uses Suomi 36rd sticks and 72rd drums, and looks much like a PPSh.
http://www.brpguns.com/categories/Ma...%252dSuomi%29/
They also have the STG43, which uses PPSh43 mags but looks nothing like it;
http://www.brpguns.com/categories/Ma...STG%29/STG-43/
You could buy one of each for what a PPSh would cost you.