I have an Olyarms .45acp upper and I own two, count 'em, one, two, magazines for it. I've never seen any more 16-round .45acp mags for sale, ever, at any price. I live 30 mins away from CMMG, they have a socom block and a set of .45acp Uzi mags that work with it, the set is worth about as much as my whole upper, well over $450 just for a few magazines.
I have thought about buying unmodified Uzi mags and busting out the welder and doing it myself. The Oly mod is just a piece of heavy gauge sheet metal welded to the back of the existing magazine, with a hole drilled in the side to take the mag release. I could take dimensions/measurements off my existing mags, which run fine, and transfer to my little weld job. How hard could it be?