here is a web site to check out for some gears. we just got home from our injection molding shop north of chicago where i was referenced to this web site. waiting to receive a new catalog from them.
www.wmberg.com
the master catalog he had, had lots of small gears. thanks for the solarbotics site. my brother has ordered from them before but i have never poked around the web site to locate the motors and gears you have found. i would love to see some pics of your truck.
my brother had some papers downloaded for electric motors for me but he has misplaced the papers. I will try to find them and post the info for you. they had pager motors for under $1 and lots of other small electronic stuff.
***update***
here is a link or 2 you might be interested in.
www.micromark.com they have tons of stuff for TINY hobbies including at least 2 different centering jigs.
www.mcmaster.com and
www.grainger.com both have TONS of stuff that is useful. tools, fabrication supplys, solder, etc.etc.etc.etc.......