There is a good supply of surplus Nagant ammo right now (which didn't exist when I bought mine a ways back). However, you can shoot .32 S&W Long and .32 H&R Magnum in them. I can tell you that .32 S&W Long is definitely a lot cheaper than than new manufactured 7.62 Nagant.
That being said, I've heard that the gas seal doesn't work quite right except with the actual 7.62 Nagant round (don't know about that for sure though).
Either way, pick up a bunch of that surplus while it's around and you should be fine.
Also, if you want to have some NFA fun with it, get the barrel threaded and put a suppressor on it. ZR Tactical up in Lafayette threaded mine (still waiting on the suppressor though). Apparently it isn't that hard to do and the Nagant is one of the only revolvers that actually can be suppressed.