I run the same thing at my local track. Im the only guy running a TC3 that is pretty much straight out of the box RTR although thats changing in a couple of days as Im adding a better ESC.
I would suggest you look for another hobby store, most places, even small joints carry AE parts. Its one of the best things about Associated, parts are usually cheap and plentiful. If one isnt reasonably close to you I know some guys get their stuff online. Im not sure where but i think towerhobbies.com is a place where a few go for parts.
This is what i would get, get yourself an extra set of arms, front and rear. Hinge pins. Extra ball cups. Extra Diff outdrives. So far ive broken those things in limited racing. The tub is durable but anything hanging out of the tub is seems a bit fragile to me. I race carpet and have been told that extra stress is probably why it seems more fragile than it should be.
Luckily all those parts are pretty cheap. Arms should be no more than 8-10 bucks, hinge pins were less than 5 iirc, ball cups $2, diff outdrives were like $8. Arms and diff outdrives came in a set of 2.
Hope that helps.