Below are links to several material suppliers that I have used for various Vintage Kart projects – Jeff Campbell

Stoners-Tools-and-Raw-Materials An excellet low price source for 6061 aluminum, a great choice for many parts.

Online-Metal-Supply has a full range of materials, everything from Phenolic sheet to Titanium .. and of course Alumimum & Steel alloys.

Industrial Metal Sales features a very wide range of Aluminum Alloy types, and stainless steel.