The Saiga forum is the best place for info on these things.
But in short, 922r relates to pretty much any long guns that would be deemed "non sporting." IIRC, on the Saiga 12, there's 4 or 5 parts that require changing in order to clear that hurdle. Any conversion will get you most of the way there, since the 3 pieces of the fire control group will be US made (the Tapco G2 model, usually you're best off buying the Tromix modified one). Toss in US made stock and pistol grip, and there's your five. Others have replaced the gas puck, which is easy enough to do anyway.
As for the magazines, the only imported ones I've yet seen are the 5 round Russian ones from Izmash. There's plenty of US made 8 and 10 round mags (Surefire makes them and they work rather well from what I've read).
As for the NFA rules, if you want the barrel cut below 18 inches, you go through the same hoops any SBS would require- fingerprinting, the appropriate ATF form, CLEO sign-off, and the $200 tax stamp (not to mention the waiting).
All this information is discussed in more detail elsewhere (like at the Saiga forum), so if you want more than this, I'd strongly recommend looking there for Saiga specific information. The guys over there have done pretty much anything and everything to theirs, so they can guide you to whatever you might want to do.