Kurt- Last year I thought about having a few made. I saw a diagram that somebody posted on here with the correct specs. I found the blanks to make the tubes in McMasters. Went to the local VoTech school and talked to the instructor. Show him the diagram and he said he could turn out a few at no cost.
I did not have him do it because of other things going on. But, I know where to go if I do end up needing some.