Bushmaster buys mags. Their Labelle milspec are great, their USA mags are crap. I believe Millett are steel, and seem to work, but I'd advise USGI, Thermold or Orlite only.
AEM , I have quite a few mags I am getting ready to sell , Milspec 30 round Center Industries , 30 round Labelles and 30 round Thermolds . All of mine are new and unused . If you are interested drop me an E-Mail . Thanks , Mike...