E-Bay - contact one of the listed vendors if you don't see what you want. They will fix you up.
Talk to a local machine shop (go there and talk to the folks face to face - calling usually ends up in a "No" response). They likely have a partial they will sell you for a decent price. If they say no - try another.
The bad thing about ordering online is shipping and handling charges. YOu can find AL for a decent per pound price, but add the shipping and it can get a lot more expensive. Going local is the way to go, I think.