So a few months ago I found this awesome website. It's http://www.teefury.com and every day they offer a different design. Once the day is over it switches out and that designs not available again on the site. They have had some pretty amazing designs and the quality is great and the prices are super fair. Check em out.…
You can find a some of the shirts they've printed in the past on this site. Although at severely jacked up prices.:) I think there are some other sites around the web that sell past designs as well. It's very scattered because the artists keep the rights to their design and put them wherever they want afterward.