There are several interesting mixed alligator+snapping turtle exhibits in North America (unsurprising, considering where the species are native), e.g. the previously mentioned California Academy of Sciences, but also other such as National Mississippi River Museum & Aquarium, Busch Gardens, Tennessee Aquarium and Forth Worth. However, the snapping turtle is a species where a large exhibit really isn't all that important, although people may think it looks nice. Snapping turtles commonly live in tiny pools in the wild and even when in larger lakes they often move very little, essentially staying at "their spot" unless forced away by a lack of food or intruders. Alligators obviously don't belong in this category, so any alligator+snapping turtle exhibit has to be fairly large
