@SteveBellovin @jonty @cstross
Beat this moose to it. (I may have a couple somewhere - unless I left them in my desk when the COVID-19 lockdown started and then turned into my retirement from Dinosaur Herding).
Plessey Mk.4 / Pattern 104 should have more than enough pins (in shell size 3), or maybe some of the Painton (small-pin) Jones connectors. The original Jones connector exists in 12-pin versions though...