I recommend first deciding what schools you may be interested in matriculating at. Then find out what showcases they are at, or better yet, do they put on their own clinic.
Targeting where you want to go, rather than hoping to get noticed in a sea of paying customers, could have much better results.
If you do find that showcase, be sure to reach out to the schools that you are interested in to see if they can take a look at you while there.
Unless you are a pitcher with a flamer, or a hitter who knocks the S#*T out of the ball on every other swing, you are not likely to get randomly noticed without the 'pre-work'.