The best source for your tubes might be Onlinemetals.com you can order lots of different diameters, wall thicknesses and materials, and you can get it in one foot lengths. There are in Washington or Oregon so they should get it to you in just a few days.
Or, you could take a set of calipers, a tape measure, and a note pad and head off to the store and see what they have in stock. Measure the heck out of what they have and go from there.
AL @ THO