Don’t know why I had never thought of it, but you might look at eBay for your bulk metal buys… there are vendors out there.
I don’t know anything about this particular listing… just give it as an example:
http://cgi.ebay.com/STEEL-PLATE-CUT-TO-ANY-SHAPE-STEEL-PLATE\_W0QQitemZ250032174797QQcmdZViewItem
