I got my tripe from "A Place For Paws", http://www.aplaceforpaws.com/rawgreenuntr.html, but they only ship to states within a 2 day shipping radius.
I think http://www.greentripe.com/ will ship anywhere in the country although I'm not sure how much it would cost, and there is also a 20 pound minimum order which was more than I wanted for one dog, however if you have multiple dogs it may not be too much. There is also a lot of really good information about tripe on this site.
I'm sure there are other places that sell frozen tripe as well, but most that I've found don't ship it or will only ship it to places really close due to the shipping cost of shipping frozen products.
You could also get freeze-dried tripe or canned tripe which could be shipped anywhere, and while it is probably not as good as fresh frozen tripe it will still provide many of the benefits.