Any auto parts store should have switches with colored LED lights in them, They run on 12volts just like your PC. When the switch is on it will be light up with your neon light If your going to put the switch where it doesnt show just buy a .99 cent switch from the hardware store, like Kitire said.
just make sure its a quality switch because youwouldnt want a .99c switch ruining your computer, i recomend getting a higher quality switch than 99c because there are dodgy siwitches