Probably not Radio Shack since they have gone or are in the process of going out of business—though if you do get lucky at one, you might be able to get the switch really cheaply.
Typically these are snap-in switches (as in you slide them into their holes and there are tabs on the back that spring out to hold them in place). If you remove it from the mounting and measure the hole dimensions, you have the information you need to find a momentary toggle switch somewhere.
Mouser and
DigiKey are two large and reputable supply places that have many many switches available and will sell to individuals in small quantities. You should be able to find something that's the right size and style and (approximate) color.
