From the sounds of it, Chester literally has nothing on show that would qualify in this category. Looking back at the argument from temperates the only thing that would apply is the sand lizards from the looks of it. At least under Temperates it had a handful of species and exhibits to hang it's hat on. Here it sounds like all there is, is a breeding programme and that's all folks. That's great, but I tend to give more weight to what's actually on show instead of what it's behind the scenes.
The aviary replacing Europe on the Edge, and large swathes of the collection displayed within the large Wetlands Aviary, also contain category-relevant species - all of which are onshow, as are some of the herpetological species which fall into this category. One of the offshow species, Montseny Brook Salamander, is a Critically Endangered species native to a tiny area of Catalonia, and Chester have bred the species on several occasions.
I'm not sure where we decided the various Caribbean anole and skink species belonged in terms of category - however even if they generally fall under South and Central America I have a feeling the species at Chester occur within mainland USA. A similar issue pertains to their Socorro Dove breeding population.
However, disregarding these the list of species at Chester which apply for this category is as follows (with offshow species in italics):
Scottish wildcat (Felis silvestris grampia)
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Caribbean flamingo (Phoenicopterus ruber ruber)
Black stork (Ciconia nigra)
Common waxbill (Estrilda astrild)
Eurasian black vulture (Aegypius monachus)
Ferruginous duck (Aythya nyroca)
Garganey (Spatula querquedula)
Marbled teal (Marmaronetta angustirostris)
Waldrapp (Geronticus eremita)
Red-breasted goose (Branta ruficollis)
Red-crested pochard (Netta rufina)
Ruddy shelduck (Tadorna ferruginea)
Tufted duck (Aythya fuligula)
Ural owl (Strix uralensis)
West Mediterranean Purple Swamphen (Porphyrio porphyrio porphyrio)
White-headed duck (Oxyura leucocephala)
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Northern viper (Vipera berus berus)
Western sand lizard (Lacerta agilis agilis)
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Lake Pátzcuaro Salamander (Ambystoma dumerilii)
Montseny Brook Salamander (Calotriton arnoldi)
Note that in terms of mainland Mexican species, I have included Lake Pátzcuaro Salamander, as biogeographically it belongs to a North American genus, but have omitted the various Mexican tree-frog species held.