ammoman.com
Aimsurplus.com

Are the two I've bought ammo from in the past.

Bulgarian and Czech surplus ammo tends to be good stuff if you can find it. You used to be able to get 880 rd crates of Czech 7.62x54r for around $60+ shipping.

From reports that I've heard, the russian surplus ammo that's available isn't so great.

In the long run its better to just reload. 6 years ago, 8x57 ammo was everywhere at almost the price of .22LR ammo, but now you won't find surplus of it anywhere.