Red-fronted gazelles: They're an AZA phase-out species with maybe two holders remaining, but I swear they're pretty much exactly what small northern zoos are looking for. They do fine alone or in pairs so no need for many acres, they can handle freezing weather, and would make a great addition for exhibits representing North Africa which is underrepresented in American zoos (source:
Ungulate Profiles — AZA Ungulates). Other ZooChat threads have talked about certain ungulate species being phased out and concerns about AZA collections being homogenized because of this as well as a few large zoos (e.g. Bronx, San Diego, Disney) monopolizing on the less-represented hoofstock species like bontebok and white-lipped deer. These are concerns I share and would like to learn more about.
Alpine ibex: Are they even in captivity in North America? They're pretty much THE thing a zoo would need to make a solid Europe exhibit. Otherwise, you'd just have bears, fox, puffins, and maybe moose (which I wish were also more prevalent, but I know why they are not) and then you'd be just as well off calling it a North America exhibit.
Hyenas: All species. They don't deserve their bad reputation and would make a great addition to Africa (or if striped, Asia) exhibits. I know spotted hyenas can stand the cold, but I don't know about striped. Few places in the US keep them. I don't know if any place on Earth keeps brown hyenas.
Asian lions: What a story a good Asian lion exhibit could tell, particularly if a zoo also has African lions.
African leopard and cape buffalo. A zoo could bill itself as having all members of the big five.