It may or may not work for you, but you should check out the S.Korean contract 30rd curved mags that Gordon Miller (HKSpecialist) is selling. I believe they are running $20.00/mag + shipping.
Many people have had great results with those mags in the MP5/Clones. Others had minor issues where tweaking of the feed lips cured them. For the price, you're better off with these mags than the Cohaire/US made junk.