Need to Pick Your Brains

I need a source for aluminum channel that is 1/8" or 1/4" wall, 1 1/2" to 3" wide on the base, with legs about 4-6" long.  Nearly all aluminum channel is wider than long.  Suggestions where I might find an odd size like this?

Solution: buy 2"x4" tube, and mill off one face.  Much faster than milling a slot from a solid block.

UPDATE: I added some code to my excavate program to calculate how many minutes each execution would take.  That wasn't hard, I already know how manyinches each motion will take and the feed rate.  When I ran the program to mill off one edge, I was appalled at the time, so it makes more sense to  remove the edge with the chop saw.  I just need to build a jig that holds the workpiece in place solidly while doing the cut.

UPDATE 2: Awesome!  One of you found 3" x4" x 1/8" u-channel at McMaster-Carr.  This gives me  a 2 3/4" slot with enough space to mount base plate casters.  Also 2"x3"x1/8" which is appropriate for ground boards of 1" to 1.5" thickness.