I don't have a part number as I just had one lying around. i also don't think they are available as a single shock. Something I noticed in the Corally WGT thread was the car they posted was using the Hot Bodies Cyclone 12 centre shock.
http://www.rctech.net/forum/electric...ld-gt-car.html
here's a link to the shock:
http://www.hbeurope.com/piw.php?partNo=61695&lang=en