For any bot builders in the San Jose,CA area there is a place that sells aluminum remnants, mainly 6061. If you pay with cash there is no minimum, check or credit card $25 minimum.
Campbell Tool & Supply, 569 Charcot Ave. San Jose,CA, 408-432-4890
Campbellmetal.com. They do not do Internet sales as of yet but they will do phone sales and ship it to you VIA UPS.