There were no "factory" hi-cap mags for this setup.  Your options are:

- USGI mags, which will hold 6 or 7 rounds okay, but more than that will bind up the mag and cause mis-feeds.

- USA's dedicated 7.62x39 mags, which look kind of like standard USGI mags without the ribs.  These are not reliable.

- Hybrid mags, made from welding an AR feed tower onto a modified AK mag.  These were made by at least 3 companies, including USA, and of the hi-cap options, these work the best, though they often need to be worked on to get them to be reliable.  These are scarce and expensive, and the only source for them will be people selling them out of their own collections.  To find them, you'll need to check the EE and the gun auction websites on a regular basis.

- Modified AK drums with an AR feed tower.  These work OK, but know that they won't feed the last few rounds in the mag.  Also rare and expensive.

-Troy

See the second bullet/listing in my list above.

-Troy