Bunnings. Pipe insulation. Silicone to hold it on, or with a bit more effort heat shrink tubing from Jaycar over the ends to hold it in place. Worked for me.
ACTROL in Brendale have the Superlon FR in 2m lengths in many sizes.
For a 1.25" tube the 1" ID insulation fits if installed carefully and doesn't slide about.
The trick to install is to tape over the end of the tube so it doesn't snag, then make sure everything is dry and push it on bit by bit ...
then heat shrink over the ends.....