Was down at the folks place this weekend, and have got hold of some thick walled tubing with about the right internal diameter. Will have a crack at making my own tool tomorrow.
The tube was formelry a 60's Triumph fork tube....Dad has lots as most of the bikes he rebuilds seem to come with worn and scored tubes.....usually with the castle nuts siezed in place or butchered, so they need replacing. They get repurposed as drifts etc. but I will see what I can do with a 6" section. According to the verniers...it ought to be pretty close.
As a plus....I also got a can of proper paint stripper....not the watered down stuff we get sold nowadays.