I am confused. Are you looking for elf on the shelf DESIGN or the elf on the shelf SHIRT? I think if I understood, you want a design to go on a shirt. I downloaded an elf on the shelf mug rug free from somewhere, but I'll have to get back to you, on that. You could just do the elf and skip the rest of the design. It may not still be free now though.....
What if you just took the basic t shirt idea and stitched it in red or green felt on your regular sewing machine, then decorate with cute Christmas buttons or stickers?