Not a zoo per se (but was probably the closest thing to it directly in the city), but the local Nature Interpretive Centre in my city (the one at the Royal Boctanical Gardens), used to have lemmings in their collection of animals which also used to consist of a Great-horned Owl, ferrets, rabbits, mice, Chinchillas, and fish being the only live animals they have now, I believe. I'm not sure what exact subspecies/species they were, but I thought they were fascinating little creatures. I don't know why they were phased out.
I didn't know about them being pets! I am on my remaining rat and I've thought about braching out to other rodents. I'll look into them.