Paul,ask the question in the general forum ( http://www.rcuniverse.com/forum/forumid_179/tt.htm ) as there are plenty of knowledgeable electric guys there who wil help you with your motor/kv/esc questions.
Regarding the spur gear then measure the shaft diameter and get a spur with matching diameter of any gear pitch to match the pinion....If all else fails then contact RW Racing- http://www.rwracing.co.uk/contact.html