http://www.alibaba.com/showroom/hot-sale-punicalagin-98%2525.html
I think at Ali Baba you have to buy in quantity.
I did a search on Google shopping and apparently it is available in health food stores:
https://www.google.com/search?hl=en&output=search&tbm=shop&q=punicalagin&oq=punicalagin&gs_l=products-cc.12...4973.4973.0.7494.1.1.0.0.0.0.0.0..0.0....0...1ac.1.52.products-cc..1.0.0.VYGpkhxZR1g&gws_rd=ssl