From my searching the only ones I have found as drop-ins for the Millenium Pros are the "Williams Fire Sights" and they are just fiber optic tubes built into the sights, not great reviews and they look kind of ugly too.
I've got the third generation PT145 (with accessory mount and no single action) and have Trijicon night sights on it. Remove two screws and pull off old sights put new sights on and install two screws (with blue locktight).
Trijicon has the old sights out and you can purchase them on ebay for under 100 bucks if you watch. I was checking with Heine about the new dovetail designs. They informed me middle of February but that is all they told me. That will be the 24/7 Pro and Mil Pro.