I just realized that I can just specify the top-level domain for the “site:” option in Google search queries. That allows me to search for DrJava on all .edu domains:
drjava site:.edu 
I have already found a few more user sites that I need to add: Purdue, Princeton, University of Illinois-Chicago, Vassar College, Case Western Reserve, Austin Community College, Wellesley College, Carnegie Mellon, Denison University, Lehigh University, California State University-Northridge, University of Massachusetts-Boston, University of Northern Iowa, and so on.
There are quite frankly too many to list them all. Way to go, DrJava!