I personally just attended the Blue-Grey Showcase in Trenton, NJ and it was a very well organized and well-attended event. Their resident hitting coach, Billy Johnson, had come to my school before to work with our players and I must say he is one of the best out there. Likewise, their staff is packed with coaches who know what they are doing.
In regards to the question in the post above, I had my coach submit my nomination form online, then shortly I was sent a packet notifying me that I was scheduled to play in the showcase. So, I believe that there is no regional tryout necessary. Rather, the Blue-Grey office will just send you and your son an information packet saying when to be there, what to do from there, etc.
Best of luck next year in the showcases!