I have used these guys for some project work and although they seem expensive, the thing I ran into from a larger bulk metal suppliers is they charge for cutting. I priced a few out here and figuring $25 - 40/cut, (some specify a minimum number of cuts if they have to cut anything), there was no price advantage and I got the real feeling that the big suppliers just didn't want to be bothered. There was never any of that attitude from these guys -
http://www.onlinemetals.com/index.cfm
The only other way is to scour scrap yards and get lucky. Used metals (esp alum and copper) are pretty pricey at a scrap places too and likelihood of finding what you want/need unscratched and straight are slim.