Glad you should ask!
I’ve spent the last four-five months painstakingly and (rather autistically) assembling lists of mammals, birds, fish, reptiles, and even plants that are available in captivity in the US- and thus fair game to use in a realistic spec zoo. Here’s a Namib desert species list that is realistic for the United States:
MAMMALS:
African savanna elephant
Rock hyrax
Cape porcupine
Aardwolf
Honey badger
Meerkat
Southeast African cheetah
Southern lion
Bat-eared fox
Black-backed jackal
Hartmann’s mountain zebra
Black rhinoceros
Gemsbok
Greater kudu
Klipspringer
Springbok
BIRDS:
Common ostrich
Helmeted guineafowl
Speckled pigeon
Spotted thick-knee
Pygmy falcon
Lappet-faced vulture
Peach-faced lovebird
Pied crow
REPTILES AND AMPHIBIANS:
Leopard tortoise (yep, this is the only reptile species held in American captivity that actually inhabits this region!)