As far as I can see they are currently listed as 'Least Concern', so wouldn't be relevant to this thread following the clarification of what the requirements were.
I know amphibians have been touched on already but the Lake Oku clawed frogs in London are really quite rare.
if you want to talk titchy small. Hows about Spiny Mice and Hopping Mice, Red Sinai/Palestina Spiny Mouse - Cedars Nature Centre in Waltham X,NE London. Dusky Egyptian Spiny Mouse - Ponderosa Therapeutic Centre Several zoo's host the Turkish and the Egyptian Spiny Mice As for the Hopping Mice, they are so far only represented by the Spinifex Hopping Mouse,held at good old Hamerton The Pebble-Mound Mice have yet to make an appearance in UK zoos
I don't know if its just an inaccuracy on ZTL but Marwell is the only place in the UK i know of having Dorcas Gazelle or Gazelles of all kinds
There are plenty of other gazelle holders in the UK - about a half-dozen places hold Blackbuck and over twenty hold Kirk's Dikdik
The nearest animal to a gazelle I could find was the blackbuck, kept at Heythrop, Knowlsey,Longleat Port Lympne, West Midland, Watatunga, Whipsnade
Longleat still did when I visited mid September, they're mixed with the macaques. They only have females as far as I saw.
Last time I saw Longleat's(with the monkeys) there were either four or five females I think. That was several years ago now.