Might be worth sending this guy a message and see if he'll post out to you.

http://www.ebay.co.uk/itm/aluminium-...5f5031ccb#shId

Also I came across this article last year, it's not exactly what your doing but it might be some help. I was wondering if you could do something similar by running 2 bike gears on either end of the roller, 2 chains between the rollers and secure the belt onto the chains somehow. It would be loads heavier but wouldn't move sideways.

http://woodgears.ca/tracked_vehicle/

www.woodgears.ca is a great website to trawl through, his gear generator is particularly useful.