Since you need only one piece of tubing, you might be able to get away with this idea and get you back to your Saturday schedule.

Buy a standard size Aluminum tube (your local hobby store) and shim it with paper. Then saturate the paper with thin CA,,, need it stronger, use epoxie or JB weld.

K&S Round Aluminum Tube 3/8x36" .016 (4)
Special Stock# LXRW78 Towerhobbie's Price 10.99
Tower has 3 different wall diminsions in this size (3/8" )

Any machine shop could make that tube,,,, not a difficult task at all,,, they probably didn't feel like setting up on that small job. The machine shop would need a 8mm expanable reamer, thick walled alum tube material, then turn the OD down to size,,, estimated time on set-up and execution, 1 hour,,, Price, $50 for that tube!

Decimal conversion; (Standard Size)

8.225 mm = .323 ths ID (5/16" = .312")

9.825 mm = .386 ths OD (3/8" = .375")

150mm = 5.900 ths Length (5 29/32 inches)

Hope this gets you going again, Willi