my dad has one in his collection, altohugh it's a super rough condition war-era one that doesn't shoot overly well, so we usually stick to the AK if we want to shoot 7.62x39.

and yea, online is pretty much the best way to go for ammo.
aside from the sites listed above, i've used/checked out these a good bit:

www.aimsurplus.com
www.jgsales.com
www.wideners.com
www.ammunitiontogo.com