They are not common, and are usually high-minimum but they are not unheard of. I believe both the french-roulette wheels that operated in Las Vegas (MGM and Paris) had single zeros. If I remember right, that's how all roulette wheels operated in the early days of gambling. Reduced the players chance by almost 3% by going to two green numbers since the payoff for a single number win did not change.

Kind of like the way 21 tables have been going... the right payoff for a player's BJ is 3 for 2. The corporate casinos are trying to improve their take by paying only 6 for 5.