I detail a lot of my plastic work on my blog. Personally I buy all of my plastic from www.sdplastics.com
, but their website is cumbersome to navigate (I just go to their showroom here in San Diego). With some googling I'm sure you can find some local to you.
Plastic forming is super simple, just cut it out with a knife or saw of your choice then heat it to shape with a heat gun ($8 at Harbor Freight). I detail a lot of this stuff on my blog. Good luck to you!