Stencils are cool to play with but the problem I see is people tend to try and let the stencil be the 'art.' They put no work into the piece. They just spray over it and move on to the next thing. But after seeing a million of the same stencils over and over I get a little turned off that they become someone's crutch. It's easier to work in b/w because color introduces a whole new level of complexity so start there. Here's a few stencil suppliers but there's tons out there:
http://www.dixieart.com/Freehand_Airbrush_Templates.html http://www.bearair.com/Stencils_Templates/departments/1103/ http://www.coastairbrush.com/categories.asp?cat=19 You could always try making your own for some variety. It's simple really. Get one of those plastic model skulls at the hobby store or at Halloween buy some foam ones and photograph them from different angles. Use a good light source and make sure the photos have a good dark and light area. Print 'em out and hand cut the darkest areas out with an x-acto knife. Probably the eye sockets, nasal cavity, around the teeth and jawbone hinge. All you need are landmarks. Then try painting the rest in. Have fun and good luck.