If you find a source, list it here with all the info you can, links, description, price, part number etc.
http://yarde.com/cgi-bin/dropzone.pl
http://www.metalsdepot.com/index.phtml?aident=
http://www.onlinemetals.com/
http://allmetalsinc.com/
http://www.speedymetals.com/default.aspx?gclid=CPquoYCA25sCFRKAxgodSyakbA
Here is a company that will cut metals to size you need. The cuts been very accurate in length and square. The prices are based on weight. They have a hub about 6 miles from me. Great service, I call my order in at 9am and most of the time I can pick it up before noon.
https://www.metalsupermarkets.com/
Here are the locations: https://www.metalsupermarkets.com/location/