We purchased a sheet of Rosco's polarizing gel a few years back for a project. We needed to reduce glare on a table without it changing as the camera panned. It worked nicely but like a lens polarizer you'll lose about 1-1/2 to 2 stops from your light source. Here's a link to a source for that:
http://www.filmandvideolighting.com/pofish19x20i.html
Mark D'Agostino
http://www.synergeticproductions.com