I make my own.
Just go to your local electronics store (like Fry's) and buy the 6 conductor connectors (RJ12 I think), and the 6 conductor wire, and a crimping tool. Cut to needed length and crimp the ends on using one of your old cables to compare polarity. As I recall they are"flipped" cables, meaning each connectors polarity is a mirror image of the other one when held side by side.
You should be able to buy connectors, wire, and a cheap crimping tool for 20-$30.