For machines find the local recyclers and become friendly with them. Learn the scrap rates and give them 50% more and you can pretty much have anything there. My collection has grown quite a bit over the last year by going to the recycler, and they let me look around without escort.
I am in Youngstown, OH. Larger cities should have larger recycling centers.
You need to check the thrifts and recyclers weekly, most of the time you find little or nothing others you get floods of good stuff.