I'll also vote for Dr. Karl at makarov.com as a source for magazines - and while you're at it, pick up one of his magazine loader gizmos for 4 bucks or so. Trust me on this, it's really a great help when you're loading your magazines. No more sliced thumbs, no more blood on your piece, etc.
Which reminds me, I just got back from the range this noon with my Bulgarian Mak. I did a quick count from memory and I think I now have 600 rounds through it and I have yet to have any problem whatsoever. 100% reliable with 4 different kinds of ammo. Of late, I'm running the green-box ammo from Novosibirsk - purchased from Dan's via makarov.com - 100 bucks for 1,000 rounds shipping included. Dan, like Karl, is a good guy to deal with.
good luck with your Mak.
Owen
Oh, and off topic, they had a .38 SPL Charter Arms revolver on display at the range. The cylinder had fractured into 4 pieces and the brass from the round that did it was swaged into the steel. I can only imagine what handload did this. The frame, interestingly enough, looked pretty good. No info as to whether or not the person shooting was hurt but I can only imagine that it was not very pleasant.