Noble Metals in Oak Ridge Tn for locals near Knoxville. They get random surplus from local shops and the labs (Al, stainless, some other metals) and will let you browse and pick - even cut, if you do the cutting. Sell by the pound.
They're a bit sketchy, so keep your wits about you. While they post prices (both buy and sell), they're not above a bit of sharp dealing. I was once offered 41 lb of Al plate, weighed and posted at 2 bucks a pound, for "just a hundred bucks, a real bargain". Cashier just grinned when I pointed out that it was indeed a deal- for them, as it was worth 82 dollars by the weight. Got the posted price.