I had meant to post this earlier, but it slipped my mind...
A very good tubular material for making grips is available, if they don't need to be all that thick. It's called Hypalon tubing, and it's marketed for fishing rod grips, in a variety of colours and ID sizes.
Available from suppliers of fishing rod building supplies - a Google using 'Hypalon grips site:au' will find local suppliers. Then of course, there are FleaBay sellers too.