If you don't have one in your case, you're not likely to find one. Alienware/Dell are the only company that make those, and they don't sell the parts. They're only installed in the new predator 2 case.
If you have the part, it's a small component mounted on the bottom floor of the case. There should be a small pcb in it. If it's the normal Alienice, there will be a small sliding positional switch so you can change all the lights to different colors. If you have AlienFX, it's a different card that's controlled by software.