Congratulations on a great caliber. I have a SAR-2 in 5,45x39 and it's a great caliber.
It was my impression that you can use a 30 round magazine in an uconverted gun.
You can't put a pistol grip, bayonet lug, etc on it without the 922r compliance. But I believe any magazine is okay.
Ammo will be back in stock in a few months. I buy mine in 1080 round spam cans from