Go to local steel supplier and see if they can cut off a piece of steel tubing that will fit.
If you have access or know someone with a sheet metal rolling machine like used to common in high school metal shops, you could easily have one made. Any high schools with metal shops or vocational trade schools nearby? Give a donation after they make it. A/C duct work shops would definitely have a rolling machine. The roller looks like this:
https://www.mscdirect.com/browse/tnp...SABEgJ6iPD_BwE