Idk if Radio Shack would sell them. A specialty electronics store might, though (I find Radio Shack is geared more towards consumer products these days). It also needs some support circuitry, so I'd check the datasheet to make sure you get everything you need. DigiKey Corp. | Electronic Components Distributor | United States Home Page
also sells them, but once you factor in shipping, it might be cheaper to get a "total package" like Nash suggested.
Depending on your experience with electronics, you might want to look into a basic PWM circuit, which uses more readily available parts. I suggested the 2575 because it requires alot less understanding as to what is going on (and thus, less "debugging").