Calico helical magazines and Bizon builds
I searched through the Bizon threads and didn't find anyone who'd scored a real Russian magazine. However, Calico's web site now lists their 50-round helical 9mm magazine for $132 and the 100-round one for $157. From comments I found on some older threads on the web, this is about half the price they used to be.
Web searching returned lots of complaints about Calico's service and back order problems, but if they actually have the things in stock now... if someone is stalled on a Bizon build, it might be worth a call.
I realize the Calico mag doesn't look quite like the Bizon mag, nor will it fit a Bizon receiver, but some Bondo to smooth it out and some magwell fangle might make one a workable substitute until the real thing came along. Or if you just wanted to build a 9mm with a hairspray-can magazine, you might not care.
The Calico mag sits behind the breech and the Bizon sits ahead, so the cartridges are pointed in the opposite direction. From the exploded views, it doesn't look like it would make any difference in the Calico mag.