Up at work we just got a nice new Xerox phaser 6250DX, which is a high end 2400 dpi color laser. What's especially spiffy about it is that it can print on paper that is 8.5" wide by up to 34.45"

long!
Seems ideal for printing out a spiffy looking marquee, doesn't it? But what material can I get to print one on?
My marquee is currently printed on three pieces of nice letter-size paper (from my own cheap color laser at home) which are trimmed and pieced together between two pieces of plexi. The problem is that you can tell it's paper, the seams show, and it is a lot dimmer than it could be because light doesn't shine through regular laser printer paper so well.
I thought it might be a good idea to print the marquee on a piece of transparency and get some kind of a translucent white film to stick behind it, but then I remembered that if I could find these things, I could probalby just print directly on the translucent white film.
So, anyone know of something that is translucent, white, doesn't have paper grain, can go through a laser printer, and can be obtained in 8.5"x35" sizes (or larger; i can trim it down)? I though of using vellum paper also, but it still looks very much like paper with the grain that is in it. I was hoping for something that results in a more plastic-like appearance.
I know there are plenty of printing services that can print me whatever I want, and I will most definately use them, but it's would be nice to cook up a custom marquee for a party or something and be able to slap it right in there!