It does not appear as if anyone makes such a cable so you may have to end up making one yourself.
Although the connector (appears to be) a standard RJ45 which is the same as an ordinary ethernet cable, I wouldn't use an unshielded cable for audio applications.
If it were me, I would cut the microphone off of the existing hand mic (assuming you never wanted to use it again) or buy another hand mic from Powerwerx. Then open up the mic and see which wires go to the microphone element and which wires go to the switch. Or the other way would be to use a meter and see which wire goes to each pin on the RJ45 connector.
Once that is determined, you can put a ¼" inline jack on the wires that correspond to Pins 1 & 2 on the modular connector for the foot switch.
On XLR connectors, Pin 1 is the ground, Pin 2 is the positive and Pin 3 is the negative. You will want to tie Pins 1 and 3 on the XLR plug together and connect this to whatever wire corresponds to Pin 3 on the modular connetor. Pin 2 on the XLR will go to whatever wire corresponds to Pin 3 on the modular connector.
Easy!