Apart from the ignition, the one lock that works satisfactorily is the petrol filler. I believe this was a Gilbern specific item. But the result is entirely academic as the filler is unused, disconnected in favour of the little foam-filled alloy tank that sits in the boot.
Following some prompting from Brian, the Club GT Historian, I looked around contemporary Fords. Lo, they popped up as MK1 Cortina.
Fortunately the Mk1 has a busy owners club. And having secured membership for thirty earth pounds, the spares secretary was able to offer a pair of matching lock barrels and some new gaskets to go between the handles and the doors - no sense in taking the handles off to put them back on without gaskets. In fact Bob was good enough to spend an hour and a half raking through all of the stock, to label the barrels with their numbers and find me a matched pair. Bob - thank you!