Hrm... Google images, maybe?
EDIT: NEVER MIND.
Try making a level in Lemmix, calling it abcdefghijklmnopqrstuvwxyz, then make one called ABCDEFGHIJKLMNOPQRSTUVWXYZ. Go to the level introduction screen on Customized Lemmings and take a screenshot. And there you have it! Well, after a long time of editing it. Faster than searching for years, though.