It seams like you already get scrap off of the craigslist free section. That's a great place to find metal containing items. You may also try your luck at estate sales, trying to buy metal items for cheaper than their metal value, although that could possibly prove fruitless. As well as getting rotors and drums at auto shops, try getting their car batteries. Near me, each battery will get me $5. Even if I have to pay a dollars or two for each battery; if I buy 20 batteries for $25 and sell them for $100, I'm pretty happy!