Most of the commercial scrap yards around wont let you in for that purpose! It sucks really because there is a large manufacturing base here and companies are too lazy to try to sell their old stuff. Or they are afraid of liability.

As far as my own scrap heaps, im in the process of cleaning my basement and frankly it is difficult as you cant clean and organize without throwing stuff out. Funny thin is i did find some stuff i needed. However much is dumpstered or donated. In the end the space is needed to build more stuff (tools & a railroad).