My best advice would be to take a bunch of materials and rub them along the tube. You'll be able to tell which one has the highest coefficient of friction with the tube.
Anyway, I would recommend
http://www.brecoflex.com/ . It's not necessarily cheap, but I'm almost positive they'll have exactly what you want.
A lot of teams used polyurethane tubing with success. I can't speak to the friction they provide, but it's probably a pretty good option for flexibility in a roller claw design.