All brands sell 16 SEER single-stage and 2-stage air conditioners.
Some brands have stopped making 13 SEER and 14 SEER units.
Trane and American Standard : The least efficient Trane air conditioner is 14.5 SEER. Ditto for American Standard.
Rheem and Ruud: Their ACs start at 15.5 SEER!
Lennox: The efficiency leader makes a 13 SEER unit, but the next least efficient is 16 SEER. It’s likely that 13 SEER Lennox model is on the way out.