You can also get polarizing film at
http://www.polarization.com/shop/catalog/index.html
One thing to note, is that some LCDs do not inverse well... Meaning that you'll get faded brown background and not-so-bright characters (at least with the green LCDs that I've played with). This has to do with the quality of the Polarizing film that comes with the LCD, the film that you replace it with, and how it interacts with the Liquid Crystal in the glass.
Unfotunetly the only way to see if it works with a specific LCD is to actually do it. The Seiko LCDs available at
http://www.eio.com used to be very good for inversion (they're sold out now)... The ones I had trouble with were the Densitron LCDs from
http://www.digisys.net/timeline/. I hope that the CrystalFontz LCDs give you better luck.
Here's a link to Arby's Inversing tutorial:
http://mp3car.com/usersites/arby/screen.html
Good Luck,
-Miles