There is an old Yacare Caiman still living at Mablethorpe seal sanctuary. Auchingarrich wildlife centre may still have Corsac Fox and Chamois.
Whipsnade have the last two Gaur in the UK. Island Amazon adventure also have a pair of Prehensile-tailed porcupines, I think also the only ones.
Someone mentioned Polar and Sun bears earlier in this thread. The rare species conservation centre in Sandwich, Kent, still feature a photo of a juvenile Sun Bear on their site, apparently being hand-reared (or checked over before being returned to its mother). There is no other information on this animal but as they have other animals not mentioned on their site such as cheetahs I'm inclined to think that they may have Sun bears, or are rearing an infant on behalf of another collection.
A couple of years ago I read that 'Amazing Animals' private collection in Oxforshire had a single polar and Asiatic black bear. Does anybody know if they still maintain bears at this collection? If not, then Dudley zoo will be the only collection to have Asiatic Black Bears.