I don't use t-slotted materials much, but when I do I buy them online from
www.Faztek.net. They have a lot of products, most of them are online for purchase too. It's really easy with a credit card and they are located pretty close to me. You can get 8' bars online via UPS. I usually only need small pieces but cut them up and keep them around for whatever. Great service too...I called them up one time because I needed some pieces machined and I received them in 2 days.