Yes, the cable runs through a plastic sleeve. Here's what you're looking for:

Dubro Flex Cable
[link=http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXD862&P=7]http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXD862&P=7[/link]

Here's a tip for using flex cable:
[ul][*] Cut the cable to the correct length using a rotary tool (like a Dremel) with a cut-off wheel. This will provide a nice clean cut with minimal fraying.[*] Tin both ends of the cable using a soldering iron and silver solder.[*] Use a rotary tool with a sanding or grinding wheel to clean up the soldered ends if necessary.[*] Solder the threaded coupler (to use with the plastic clevis) on one end and solder the metal clevis on the other end.
[/ul]

The purpose of "tinning" the ends of the cable with solder is to keep the exposed cable (outside the plastic sleeve) stiff. I use this method all the time and it works great. Good luck!