U.S. Equivalent of French T80 for Sourdough Pain de Campagne
You would want to look for a high gluten bread flour, in the 14% protein area.  I found this helpful for understanding different flours.  In the Fresh Loaf Discussion Forum, a user suggests combining whole wheat and bread flour in a ratio of 80/20.  

Here in the US, you probably have access to King Arthur flours.  Their whole wheat is 14%, white whole wheat is 13%, and bread flour is 12.7% protein.  I doubt you want to go 100% whole wheat flour, so you could use some of the information I provided to create a blend that would work well.

It looks like you could also order from French T80 here. Although, I should point out that this product description is a little confusing because it describes T45 flour below, and a protein content of 10%, but you might be able to contact them for the product you desire.