Gun Broker might be a source, but as I recall Ebay limits magazines to 10 rounds, so you're not going to see the standard capacity magazines there.
Are you in a 10-round limited state?I'm looking at the same issue. I may have to go with the 10 round Mecgars that are currently available at a reasonable price. I would expect the quality to be good, considering they're Mecgars. For the price, $26 as opposed to $60+ factory, I suppose I can live with the reduced capacity.