Watch the NRA course website. Just checked within 500 miles of Franklin, MA — two classes offered- one in MD, the other in PA. Both June 15th. Am sure not helpful.
Not a lot of demand for shot shell reloading classes - since shot shell reloading is 100% formula from a manual - XXX brand hulls, xxx brand wads, xx gr of XXX powder, X.X oz of shot. Most people learn what they need from other shotgunners. Second issue you will have is being able to make it worthwhile for an instructor to run a shot shell reloading class. Lastly, if you are looking to become an instructor, there are not a lot of NRA training counselors that are certified to teach the course AND can pull together enough instructor candidates to make it worth their while.