I’m sure you’ll learn about summer programs through your music department. There’s certain to be a bulletin board with all the notices. Some that come quickly to mind:
Atlantic Music Festival https://www.atlanticmusicfestival.org/the-institute/programs/composition-program/index.html
Nief-Norf: http://www.niefnorf.org/composition/
EAMA http://www.europeanamericanmusicalalliance.org
Fontainebleau: http://fontainebleauschools.org/music/index.html
California Summer Music: https://www.csmusic.org/index.php
Brevard: https://www.brevardmusic.org/institute/college/composition/
Music on the Point: http://newmusiconthepoint.com