From Monday 18 January the SM19 service from Epping Station to Harlow via Thornwood will also run on Saturdays along a route which has been extended to Ongar. [Information from Essex County Council’s Bus Passenger News.]
You can find out more about local bus services here and at Traveline (tel: 0871 200 2233). I’ve also found this independent website useful for Epping to Harlow journeys.