There must be more sites than the one I'm listing here available to us ...but my machinist showed me this site when I was looking for a couple of aluminum bars and didn't want to drive all over town.
www.onlinemetals.com
Those (4) 1.0 x 1.0 square aluminum bars (x 9.0 long) used to lower the A-arm spring pans on a '55 or '56 can be ordered "cut to length" - and all you have to do is drill the holes.....
Steve Metzger Tucson, Arizona