I am just getting back into wood working I am going to try and find a supply like this for building my tool stands/ cabinets.
I work at a retail store that sells "everyone's favorite tool brand" and you would not believe the stuff we throw away, appliances, exercise equipment (all kinds of shapes and sizes of tubing) old shelving and so on. Company policy it must be thrown away no keeps...so not really a resource but if I could I would haul lots of stuff home.
+4 on the appliance sheet metal! Best place to find fridges, dryers and bedframes is in the 'free' section of your local craigslist. There are usually several listed at any given time! The sheet metal is at least 18ga and the 90* reinforcing bends make great edge material!
When I lived in the midwest there was a junkyard with 1930's to 1950's vehicles west of Omaha that we used to get our parts from. As far as metal and hardware I would stop at the Boeing surplus store in Wichita KS. I still have some scrap aluminum left over....that was over 20 years ago.....