Only thing I am aware of is the CARM mags.https://www.carm-magazines.com/high-capacity-carm-magazine-for-pp750-air-pistol.aspx
I find it amusing that the point of 3d printing for many is that is decentralizes designing and manufacturing. the files can be designed anywhere and printed anywhere.So I’m amused by relying on the postal system.Of course it’s the same for buying filament.The guy who designs and prints and sells the carm magazines is of course free to market his stuff however he wants.