Update...
Turns out Lighthouse have actually got them, they just have not got them in their "index".
I hunted them down on an american website ("vintagejeepparts.com") which appears to have an amazing selection of old model jeep parts but which doesn't ship to the UK....
But they quoted a part number for the cable i wanted, so I phoned Lighthouse and asked if they could get one from anywhere, and lo and behold, they came up with one they had on a shelf but not in their "system" (and they were cheaper than Vintage Jeeps as well....).
Done and fitted and a nice refurbished heater fitted and working! Success!
