That was basically a substitute for the normal twistgrip throttle, so you should be able to substitute with one of the usual eZee throttles which may even have the correct plug in termination if you are lucky.
You should be able to get a spare throttle for one of the earlier F series bikes (Forza/Forte) from the UK agents
Onbike. In fact it's probably the same one for most models. Some throttles have a five way connector since they include a rocker light switch, others were just throttle only three way connected.
The three connections are the 5 volt live feed from the controller, negative, and the increasing voltage return signal from the EAF or throttle. You will have to check out which is which with a meter and, if necessary, provide a suitable connector or revise the connection order in the one supplied.