Journey End has courts, as does the Essene Way. There used to be courts at the high school, don't know if they are still there are or not. Caye Chapel Golf Club is building courts. In Placencia Inn at Robert's Grove has courts. I believe there also are courts in Belize City at the private Pickwick Club. But tennis isn't big in Belize.
Belize First Magazine http://www.turq.com/belizefirst/