When you look into grips, check out this guy from Budapest
Hungary, I bought a set for my FEG PK knockoff named a SMC-918. It also fires the Makarov round but is not as nice a gun as your P-64. Yours being all steel construction.

His grips are very nice and my pair had beautiful crisp checking.

His site is worth a look when you get serious about buying grips.

http://www.marschalgrips.com/