They can give you some stickers from their PAO fund...or you can take their images, edit them and print them on sticker material (pick it up a office max or CompUSA). Make your own stickers in any size....
when i am looking for hard to find stickers or unique stickers I go to car and truck stores (I.e. but not limited to pep boys). I have these shops like the fast and the furrious by me and they have all kinds of "window stickers"
the one on my jeep is madusa. (greek mythology) if you look her in the eyes you turn to stone. I got that one at pep boys. I will give the best "risky" sticker spots.
head shops and dead head stores. They have books to look thru. all kinds of different things. I will post my grim reaper hummer soon. (bill and teds excellent adventure)
Or you can cut out an image, tape it to the outside, trace the outlines with a fine tipped sharpie on the inside and then paint it in by hand.
Then paint the rest as you normally would.
I painted this Taz for my BRP Buds car a few years ago, can you tell it was around Christmas?