There's a recycler around here that gets some good stuff in every once in a while. Several months ago he got a '69 HP 440 block. I offered him scrap price and he refused, said he doesn't like to sell stuff. Went back the next day with a hundred in my hand and he changed his mind pretty quickly.
I've seen it both ways. There was a scrap yard in Waco that we could buy anything out of the engine pile just by setting it on their scale and paying by the pound. Half the engine blocks, cranks an heads on engines that ran at Heart of Texas speedway in the early 70's came out of there. One scrap yard up here thinks that everything he has is worth the same or more than new and the other place won't sell anything to the public. I haven't tried to buy anything from the big new one yet but I think they will sell stuff by weight.
My scrap guy happily sells me anything I want for a price per pound. And not anywhere near what they pay me for my junk. But I usually ended up getting a better deal. Picked up a set of old chrome steelies last Summer for $20 and sold then ten minutes later for $200. You have to be a scrapper to buy from the scrapper. If they open their doors for people to go dig around, insurance would be so high they would have to close down. I usually try to make friends with the crane/magnet/yard guys too. A case of beer can sometimes get you whatever you want, just take it out of your weight when you re-weigh.
I have a buddy that works for the local scrap dealer. He says that they will not sell used parts because if they break and cause an accident they could be sued. I've tried to buy lots of stuff, even tried using the old case of beer to employees to try to find an "in", no dice.