If it's any help, I replaced mine many years ago with sections of 1/2" (12.7mm) standard copper water pipe, painted black.
It is exactly the correct outside diameter and the advantages are that they cost me nothing, were very easy to make, and will never rust.
Only disadvantage is that the wall thickness is much thinner than the original, however I've had mine on and off several times over the years and the reduced wall thickness has ever been a problem.
I actually upgraded the bolts on mine to 5/16" UNF which allows you to tighten them up a little harder, and may or may not add to the rigidity of the assembly. Admittedly, I mainly did this because the female threads were in poor condition, so it enabled me to cut new clean 5/16" threads.