Yeasu does not use the larger RJ-45 Ethernet connector, they use a small telephone like connector RJ-12 (6 pins unlike RJ-11 4 pin for standard phones) Like I said Radio shack does carry the 6 conductor stuff.. not much and you have to be careful you get the right stuff but they do usually have an extension or two that can be used as a start of the extension. the hard part is the straight through barrel connector. The 6 pin couplers were all crossovers. I popped it open and rewired it to work.
This photo shows what I did for my ft-8900https://plus.google.com/108388273845581073968/photos/photo/5719425459274729634
EDIT: above link does not show photo I wanted to show.. lets try this:https://lh3.googleusercontent.com/-tpHoCmwk8rI/T197JwNlSKI/AAAAAAAAB7g/FpGmtHmRPhc/w950-h710-no/2012-03-13_12-25-04_586.jpg
If it uses a standard modular plug like an Ethernet cable, I just ordered a Cat5
cable from DigiKey in the desired length, color and configuration. (I got something
like a 14' coiled cord for my IC-208, giving me plenty of room to pass the mic around
my van.) There are lots of other sources as well.
Just unplug the old cable from the control head and mic and plug in the new one.
The only issue was determining whether I needed "straight-through" or "cross-over"
connection, which involved looking at the color coding on the ends of the existing
cable (or testing it with an ohmmeter.)