I used a small geared motor from this place for my motorized USB drive. http://www.hobbyengineering.com/SectionM.html
They have motors in small to medium sizes. They have motors with gearboxes attached and you can pretty much choose the RPM of the output shaft.
I spoke to them when I bought mine and they were very helpfull and knew what they were talking about. I got it fast too.
That looks like an incredibly cool shop, thanks! I may resort to overseas ordering if local sources fail. They got what I need ready made, Tamiya, and cheaper than the bare gear set I had in mind. Except shipping, unfortunately. Still, a great outlet.
In fact, I'm starting to entertain the idea of importing such goods and reselling them. Whatever is available here comes at exorbitant prices, and many are simply unheard of, like chain + sprocket assemblies or pulley kits.