Unfortunately, no such magazines exist in quantity for a rifle such as you envision. I don't think Kel-Tec wants to get into making a lot of specialty magazines.
It shouldn't be too hard to make a modification of an existing kel-tec design, if you could secure a large quantity of magazines from the east block for the PPsH for example. Have them make a couple of thousand up on special order.
The problem is that these type of guns are already flying off the shelf, and there is no production capacity that is not being used already.
All good points. It won’t happen. But let’s just say that there were millions of good PPShK mags in eastbloc warehouses....and millions of sealed spamcans....and they could all be imported for a song....it’s an interesting thought experiment. KelTec could readily fill a “niche” considering the superior ballistics and much much lower ammo cost compared to 9mm. At this time, 9mm costs literally 5X tokarev ammo.