The Broken Hill Explorer operates weekly on Mondays from Sydney...There is a PDF timetable freely available for all Western services. The coach Dubbo-Broken Hill runs daily via Cobar, including the days that the train runs. The only station between Parkes and Broken Hill served by road coach is Condobolin, 3 days per week, while four other stations only get the weekly Broken Hill Xplorer.
The bus operates on other days.
The clunky NSWGR website refuses to supply a pdf for the bus....suffice to say its 3 hours longer travel time than the train.