David, Just a couple of questions regarding the brake light.
Are you replacing a pre-existing one that is not working or broken?
Have you considered other types of third brake lights?
I ask because I did this on my SC that had a Carrera tail. It was a major PITA.
I had to remove the deck lid first. Then I had to remove the tail from the decklid to drill the holes. The wiring is fairly easy.
I bought mine from Hershey one year for $20. I'd try calling DC Automotive. They can usually get obscure parts like this. Be warned though, they break very easily at the neck.
I am currently running an LED third brake light from Pilot on my Carrera. It attaches inside the car at the top. }{arlequin is also running the same light. I'll see about posting pics tonight.