When I travel I always like to seek out beer that is not available to my favorite local bottle shops. One tool that I've found to be helpful is the Seek-A-Brew website.
From the main page, if you click on the Beer Distribution Map, at the top of the map you will notice Display brewery on map: Select a brewery. Click the pulldown menu, find a brewery, and the states this brewery ships to will be highlighted on the map. For example, I will be traveling to Arizona soon and now know that AleSmith, Lost Abbey and Crooked Stave do ship there. And Hair of the Dog, Wicked Weed and Hill Farmstead to not.
If you click on a state on the map, a list of all the breweries that ship there will appear. The list can be sorted either alphabetically or by the number of states they distribute to (ascending). This could be helpful to see the most limited distribution to a state.
Note: A brewery may not be displayed if shipping is limited to a state, for example Maine Beer Co does ship to Maryland but only some of their offerings, and thus does not display on the Beer Distribution Map.