There’s one in town here. I’ve talked to the owner, (pre-Covid) and they buy them by container load, basically sight unseen. They fix up what they can fix up, and sell a lot of “as-is” bikes to people looking for/who don’t mind a project. They also sell the basics you might need to get something to roadworthy state (tires, chains, brake pads, 7,8,9 cassettes, etc).
I never bought from them as I always thought they were asking a bit too much for the bikes they had, with the work that needed to go in. At least one friend gets a lot of his parts for his builds through them.