Watch buying off of EBay. Lots of stuff listed, and lots of stuff not exactly kosher.
I bought a bunch of what "looked" like factory Colt and GI mags off there, and once I got them, it was obvious that all were counterfeit, or not correct. Pay close attention and ask a lot of questions.
One thing with GI mags you need to watch, there are counterfeit mags out there, and there are "surplus" mags that are not in spec. Just because they are "surplus", doesnt mean it was a surplus/overrun of good mags. They could be rejects that were refused, and are being sold as "surplus". Ive run into that with mags, bullets, and a few other things.
Good, original GI mags were always my best bet with my 1911's. Colt mags are usually good too. Regardless, you still always have to proof test them, no matter what they are.