www.redbubble.com/people/OurBigBook/shop (case insensitive) has a marketplace mechanism 6.64 pound/unit for the 21cm size, which is quite expensive. It is unclear how much they pay the creator.
TODO: the following links are currently restricted because it is a new account:
stickerapp.co.uk/ does not seem to have a marketplace, 2 pounds/unit on an 11 unit order, so much cheaper. But why would we need 11 is the question. Just going with the marketplace for now.