I recently had a chance to visit on of my favorite places Sim's Recycling resale yard. You never know for sure what you're going to find but there's always something interesting. Here are a few phone photos from that trip:
This is a large bin of large chunks of solid copper. I'd love to load this up in the back of my truck.
There's no shortage of aluminum here. There are several large racks of billet aluminum. Pretty much anything you could need from a few ounces to hundred's of pounds.
Does your project need a few or a lot of giant casters. If so, this is your place. I'm not sure where they came from but someone had a lot that they decided they didn't any more. Almost all of them are in excellent condition and are available by the pound.