I used these guys but my understanding is that you can buy the movement and install it yourself. I had taken my instrument cluster in to these guys to have the printed circuit board fixed so it made sense for me to just have them do the clock while it was there.
a friend did buy one on ebay for his Charger and the one that came was for a Vette or some **** so last I knew he returned the wrong one and his clock still doesn't work....
I believe in hiring things done by those that specialize in it if it's something that falls outside my wheelhouse, I don't have time for B.S.!
http://www.bobsspeedometer.com/1/120/index.asp