Go to: http://gameconsolesupply.com/posters.html They have any poster you can think of! All for great prices!
You can buy stencils for tracing at places like Michaels and winners. You can also buy from Ikea dependent on what kind of stencils you are looking for.
You can buy lettering stencils at Stencils Online for a great price. Additionally, you can find: custom stencils, decorative wall stencils, alphabet stencils, and stencils patterns.Check out the link below for more details.
You can buy spray paint stencils and a number of other stencil designs at Stencils Online. Also, you can customize your spray paint stencils into any design or logo you want. See link below for details.
Anywhere that there would be antiques
One can purchase plastic letter stencils from various websites like Amazon or eBay. Both websites offer a great list of different plastic letter stencils for cheap prices.
Usually for a booklet of stencils it costs around $10-$15.00 if you buy them from a online store. There are, however, sites that offer free, make-your-own stencils, like this one here: http://www.suite101.com/content/free-pumpkin-carving-stencils-a149319.
You can buy a Hollywood Undead poster and other items at their website.
There are a few stencils for sale at some of the board shops, like http://www.360skate.com/search1.cfm?Search_Term=stencil Here is also a little short version of the instructions for making a stencil that might be interesting for you: http://www.bones.com/bricabrac/stencils/
There are many Halloween stores online that sell Jack o'lantern stencils. Also, around Halloween time your local Wal-Mart or Target should have them in stock.
The Scarface poster from Friends is a widely distributed poster. You can buy one like it at Walmart or on Amazon.
The website below has a good selection of printable stencils. They have 20 that you can print directly from their site including a bat, cat, skeleton, spiders, and of course pumpkins. Additionally there are a few other links that provide more Halloween stencils. painting.about.com/od/freestencils/a/stencil_hallown.htm
Yes, you can definitely print pumpkin stencils from the internet. You can downloand and print for free at http://www.rd.com/slideshows/12-free-printable-pumpkin-carving-stencils/ or http://www.extremepumpkins.com/pumpkin-patterns.html