You could try Spoonflower. They make custom fabric. It might be a little bit expensive, though. I also recommend going to second hand shops.
Interested in commissioning a costume or accessory from me? Go to my Facebook page for more information
Alternatively, order an accessory or some clothing from my Etsy store.
Etsy Deviantart Blog
Currently Working On:
Female Titan (touch ups);
Daenerys (Game of Thrones), Hannah Alexander's Art Nouveau Sailor Moon (long term project), Marianne (Brotherhood of the Wolf)