I'm not sure if this is still available or a viable option but when I was in college, I worked at the airport gassing planes. We used Meguire's Mirror Glaze on the plexi airplane windshields. Did a great job! Rub it on till it was almost gone (into the rag) then follow up with a clean cloth to buff out.
This won't really apply to us but we were instructed to always apply and buff in vertical strokes up and down the windshield. They didn't want any swirl marks that would scatter sunlight.