Robin,
There's an Australian mob that make super-high quality CF tubes for the Oil & Gas industry. Before anyone starts groaning
, they are MUCH better by any measure, than anything commercially available for telescopes. I doubt they would be particularly cheap, but they produce tubes in standard sizes that should be adaptable to your purposes.
I SHOULD have their name directly to hand, but its lost in my other PC somewhere.
Will PM you their details if interested.