I have a Universal Ferret.
It's hard to find ammo for it. It's easy enough to form .357 mag to .256 WinMag, but suitable bullets are hard to come by. Hornady makes a flat point, but they hang up and don't feed. Any others are too long. So, my solution was to buy bullet swaging dies and a press. The next problem is finding bullet jackets. Long story short, I can make some bullets comparable to the 60 gr. hollow points that Winchester produced in the past. Sometimes you can find the factory bullets and loaded ammo, but it's pretty expensive ("collectable", I guess).
The magazines are made out of plastic. They are hard to find, too. Years ago, you could find them on the auction sites. I think e-gunparts might still have 'em. I tried to modify standard M1 mags, but that didn't work out too well.