You didn't say if you want full color, or black and White type cartoon line drawings. Or even the subject matter. If you want it to be on the both sides of the hull. First you can check out the ones the plane modelers have already made up at the hobby shops or sites. Or look though the clip art disks that come with those print shop programs. If you find one you like take a copy of the file to your local sign or printing shop that has a color printer/plotter cutter. tell them what size you want and they can can print it out and trim to fit.
RC cars have a lot of vinyl stickers/paint masks kits or sheets that they use to paint the designs on the in side of the poly carbonate/lexan bodies.
Another source is the pattern books for other crafts or clip art books on most any subject you can think of. Say from Dover books. they have some great ones and I have used them for sign painting for years.
http://store.doverpublications.com/ there is a supplier that has a site in the UK some where but I can't find out were I stored the addy at