You can steal the wallpapers from a Snow Leopard machine if you know where to look. It really isn't all that difficult to copy them over.
BUT... since I no longer have a Snow Leopard machine up and running I can't personally do it. Google perhaps?
EDIT: Actually... I might have a Snow Leopard Server virtual machine installed somewhere. I'm not sure if the Server version has all of the wallpaper, but I'll look tonight when I get home.