There was a documentary years ago about how Shadow found the albums that he used to sample and make Entroducing. According to him, a record store in SF has tons of old dusty records in a basement and the owner would let him go down there and dig through them. The documentary is called "Scratch". It's a documentary on DJ'ing and features Mixmaster Mike, Q-Bert, Shadow, Cut Chemist (Jurrasic 5), and the pioneers like Kool Herc, Flash, and more.