Chris,
It doesn't have to be shielded, if that's your worry! There is NO AUDIO on this cable. One pair of wires is used for the PTT switch. Just a simple switch to turn the transmitter on and off! The other two wires are power and ground for the map light, which you may or may not have installed. The "shielded" quality may add redundant strength in this case, but has no affect on the circuitry, or the quality of transmitted or received signals. I have even seen a 2 conductor cable used, with the shield as common ground for both circuits.
Does Cessna not have it? Good luck finding the "right" cable if Cessna no longer carries it, or you don't want to pay their rediculous markup!!