What kind of metal? I bought my T-slots in a one time deal from a guy who sold his extras. I buy aluminum plates cut to size off of Ebay. Try Ebay section - Scrap Metal. Sometimes you can find "cut to size" there. A friend of mine goes to junk yards that specialize in scrap metal, but I have nothing like that around me. For small pieces you can try a hardware store (Thin 1" or 2" square steal rods and tubes, 4" wide steal plates about 4' long, etc...) And then there is the retail route. Most cities have a company that will sell you 1/2" aluminum plate, but it will cost you bucks unless they let you have seconds which you should always ask about.