Wym at AMC somewhere down devon is the man in the uk for all twelth
http://www.actionmodelcentre.co.uk/ 01803 666556
kimbrough spurs work great use those that fit the tc3 69,72&75 i think
most people at nationals run the zytec its a bit more agressive than the p35, but not as bad as the cefx or crc
rollout is calculated by (tire diameter*pi)/(spur/pinion) there is a full spreadsheet out there somewhere but i aint got a clue where
round by me there is chesterfield but we normally have a few month break till we start back with the rugrats as the nats run oct thru march