Someone once told me they were a variety of madsen mag - a large distributor was selling them for $5/ea. Someone then realized they made good 9mm ar-15 mags and they disappeared from the market. A bit later, JLD Enterprises started selling the converted mags for $35/ea and then I think $45/ea before they finally ran out about a year ago. I got two, and they worked better than either coverted uzi mags or the straight "argentine contract" 40 rounders CDNN was selling, although they do look a bit goofy at first, since a straight mag is the more traditional look. JLD was the only place I've seen sell these in volume, and they've been out of them for a year.
I am probably gonna sell my 9mm AR to fund an F/A purchase as soon as I can find someone to sign a form 4 for me. I was gonna keep these because they are somewhat unique as well as my colt mags, but now I'm thinking I'll just sell everything. If I do sell the gun, I'll send you a PM about the mags, if you're interested.
Rocko