At the bigger gun shows find the guy who just sells magazines.
We have a guy, Phil, retired PO from NY who comes to the local shows in PA. He only sells magazines & grips.
The military contract mags that are grey parked and come in a plastic bag, they are rapped in an aluminum paper and date 1980's. They have the contractors number on the mag base versus makers letter on the base toe like the WWII ones. These can be had for $8-10.00 each buy the 10 you want they work and they go bang every time.
Good enough for the killin' fields good enough for the range right?
Adam