they're John Masen 10-round mags, i got them from Midway USA.
They are pretty cheap but they seem to work pretty well. I have four of them, they always feed all 10 (they also will load into a closed bolt, and not obstruct charging loaded with 10)
I spray painted two of them flat black (to give make them look more like the 10-round M14 mags my father uses in his M1A)
http://www.midwayusa.com/product/461...55BrandPopProd
I have a couple of old high-cap mags, but they aren't very reliable and need to be repaired.