Now that ISIS has closed its doors to public perusal, its harder to make a tally, but I believe the Dianas in the UK are still roughly as follows;
ZSL. 1.2.
Exmoor; 1.1 or(1.0). mother & son? from ZSL but have no idea if related to current ZSL animals.
Newquay; 0.2(sisters, remnant of a larger previous group of six) a new male was obtained from Port Lympne but apparently they killed it the week it arrived. That was several years ago now and there has been no replacement(afaik). Difficult to obtain another one?
Paignton; productive breeding pair were split up, 'for genetic reasons' and the male sent away. 1.2(or 2.2) offspring- 0.1 escaped and was killed. That leaves Mother and 1.1(or 1.2/2.1?) offspring? No new partner has yet been obtained for the adult female to my knowledge.
Port Lympne. About four. Maybe one breeding pair+ offspring.?
That's the total afaik. If its difficult/impossible to find new partners, why not centralise the unmated animals in one group somewhere? Answer; too radical and some zoos would lose their exhibits.