Where ever they can be found. There are not too many gun stores up here that know everything there is to know about milsurps, so I can still find them in gun stores. I have picked up a few in Uncle Henrys over the years, but the bargains usually go fast. But most of my C&R purchases are local gun stores that get a lot of trade-ins.
I have bought a few things online from the auction websites. When I do, I always ask the seller to keep me in mind when they have any other similar stuff to sell.
My best steal was at the concord gun show believe it or not. nagant pistol for $80 when they were selling for $95 plus shipping from the dealers ($120). Russian non refurb worth ~$700, paid $425. Gunboards is great for C&R but the best deals last about 6 minutes from time of post. No time to think about it gotta be fast!
My best deals are had with private sales. Estate sales are always good too. if you use GB or AA your up against the entire country. If you belong to a club talk to the old timers. You would be surprised what they have closet or under their bed. Usually for 30 years!!!