Acquiring Solar Sprint PV Panels and Motors
Pitsco (1-800-835-0686, or http://www.pitsco.com) sells Solar Sprint kits. They supply a panel/motor kit (Catalog number W21210, $44.95), and also a "deluxe" kit for $54.95, which includes some gears, axles, and wheels. Their panel is pretty rugged, but expensive. The package of hardware is pretty poor.
Solar World also sells motor/panel set ($29.95), and a gear/wheel set ($3.95). Their panel is a little more fragile than the Pitsco, but far cheaper. The hardware package is of far higher quality than that from Pitsco.
The motors are cheap, 3-volt hobby motors, a pretty good match for the panel. If you are interested in a faster car, you might consider buying a better motor, as the official motors only reach about 50 percent efficiency at most.
Sources of PV Cells
solarcell.net has some very inexpensive individual cells, including some very high efficiency "space grade" cells.
Electronic Goldmine has a variety of individual cells.
Herbach and Rademan has a variety of individual cells.
Other Sources of Solar Educational Kits
SunWind has a variety of solar car kits and small PV components (and some nice general solar experimenter's information).