Is there a map or chart that depicts the areas of the US that are most prone to hailstorms?

Don't know, but it would also likely be associated with areas consistently experiencing major heavy thunderstorm activity and maybe tornadoes. Hail requires fairly violent weather.

At any rate start with these folks. NOAA's National Weather Service There are also likely some Universities specializing in weather prediction, or extreme weather studies. You might try finding some of their sites. Also, simply search on "hail".