Pretty certain you're talking about a positron cable. Be careful. Positron is a SOLID cable, not like other bike cables. It pushes and pulls. And I got mine from someone here... He sells on ebay too.
If it is your Positron (derailer) cable, you got good advice. It is a special animal. In the event that you do match it, you can get gray cable sheath from US Choppers that is really close so's you can freshen-up the others. :wink: