By default, the front-end campus selector will show campuses used by events in the current group/view.

You can override this to show specific campuses on a per-group basis by adding this to your public.config.php file.

$_LW->CONFIG['CALENDAR_GROUP_CATEGORIES_CAMPUS']=[ // custom campus types to display on group calendar(s)
        // Group ID => Array of campuses
        1 => ['Campus 1', 'Campus 2'] 
];