No PWA stuff here, but as some others have said, there are grass-roots events with varying levels of organization in New England, Cape Hatteras, Florida, Texas, San Francisco, and The Gorge.
The highest level of freestyle and wave sailing is in San Francisco (where they have the "King of the Bay" freestyle contest and a fair sized formula / slalom fleet), and in the Gorge (where they have the "Gorge Games" and "Gorge Freestyle Frenzy".) They may also have some wavesailing contests in Pistol River, Oregon, where a lot of the Gorge sailors go to wavesail.
The best place to find out about what's going on in American windsurfing would probably be the forums at www.iwindsurf.com
or the windsurfing magazine website www.windsurfingmag.com