There are a number of graphics programs around that include black and white raster and vector images that could conceivably be "colored" in with crayons or pencils once printed out. Some to check into would be Hemera's Big Box of Art, Broderbunds' Print Shop, online downloadables would probably be www.clipart.com. As to "adult" specific, that I don't know ... it's pretty much wade through and see what turns up. I'm sure you'd come up with a good deal of silhouette type imagery.