Any one got any ideas as to how to identify the frequency for the lock/unlock function? And if I do, how easy is it to find another transmitter at that frequency which controls a simple on/off switch?

Model unidentifiable though I am informed that UK models of this make only used two frequencies, 315 and 433 Mhz

US models however used different frequencies. Curiously enough people say that the 315 and 433 Mhz fobs can be bought but the mysterious american ones can't. And that since the car was built in the mid 1990s, technology has moved so far forward (on a simple on/off switch??) that the technology is obsolete and new fobs are unavailable; and that I have to buy another receiver unit and matching fob at a cost of $600!

Does this sound plausible?