Maybe you can post a couple of wallpapers that you like as examples.
I haven't really looked at wallpaper sites for a while now (I do download them if I come across them.
Did a quick google search and it is more difficult than I thought (didn't look at the image search results). It's probably easier if you have a specific character, series, artist or company.
Did you see this one?http://wall.alphacoders.com/index.php?s=comics
I personally like this site for looking at art, but most of the images are not big enough for a wallpaper...http://comicartcommunity.com/gallery/index.php