You can get some great stuff at a good motorcycle dealership or cycle supply. Just look for the number plate backing. I believe N Style is the most common brand and for about 15$ you get 2-3 sheets that are approx 12x14". They carry, white, black, clear and simulated carbon fiber usually. I run that stuff as its the same thickness as Losi or Jconcepts stuff and its way cheaper.
Team Losi XX-4 WE, XXX-4, XXX-CR, 22 2.0, 22-4
"Dudes on the left for hi-fives, girls on the right for making out!"