I don't know. As I said, the most recent TSA documentation says 68 airports have MMW in PreCheck. They don't provide a list of which airports those are, and I don't think there is a current list publicly available.

I do know that there are some heavily-used airports that don't have MMW scanners in PreCheck - LGA, for example. As to why, unclear. TSA does not share their reasons or roll-out schedule with the traveling public.