Hmm, not some across any superhero print fabrics - at first I thought you wanted to make a superhero costume, and I know just the place for that:
http://www.whitelodgefabric.com/engine/shop/index.html
Lots of lycra and spandex (nice. :shock: ) alongside some more, er, popular dressmaking fabrics.
Good luck with your hunt - I want to see pics of the finished quilt! :-D