Military contract magazines were made by many different suppliers. I have a bunch of Center Industries mags, as well as a few Adventure Line examples. In rummaging through my magazine drawer, I also find some Sanchez Ent. and DPMI brand. The part number on these should be NSN 1005-00-921-5004, at least that's what is on the bags of my new magazines.
I avoid 30 round magazines not manufactured to military contract, since I've had so much trouble with them over the years.