You have it right, most teams use 4 cims in the drive, two per side, installed in one transmission.
There are a lot of wheels, look at AndyMark's web page
http://www.andymark.com/Wheel-s/229.htm
also IFI (now VexPro)
http://www.vexrobotics.com/products/...on_vexpro=4536
also some teams make their own, or adapt other wheels to fit robots (both of which takes some effort).