You could try buying a copy of "Galaxy Angel EX." It's mostly a collection of minigames, the goal being to earn enough points to unlock wallpapers. Then there's a function in the game that allows you to set one of the wallpapers you earn as your own wallpaper.
Does that help?
Galaxy Angel EX only provides SD resolution wallpapers, with the width/height ratio of 4:3.
I suggest the OP to visit sites that provide wallpaper galleries, or image boards. Angel-Tai.com
would be a good first step.