St. Louis has 3, last I visited in October they were off exhibit but I still got to see them because it was a class trip and one of my classmates is a part time reptile keeper there.
The tuatara kept in St. Louis and San Diego are kept off display. Toledo Zoo has tuatara on display (which is where I finally managed to see one).
Saint Louis sometimes has them on display. The San Diego Zoo is the only zoo outside of New Zealand that has Brothers Island tuatara, unfortunately off display.
