Just to follow thread940-1718710 it seems the part needed is
700439268 BM12/SBM24 BUTTON MODULE TO 96XX
REPLACEMENT CONNECTOR CABLE
As I couldn't wait to source one I found a tip somewhere else and just cut about 2mm off the corners of a standard RJ45 plug which did the trick.
I did use a cable tester as it needs some care not to cut into the wires.
