you need to take a bus from Mao which you can get near the park in the center of town to Santiago, Once in Santiago ask where the bus to Bonao is, I believe it is directly acrooss the street from where the bus from Mao will drop you off.
Parada Bonao / Santiago, is located at the parking lot of " El Guacalito". (publics offices building) Corner of Av. 27 de Febrebrero and Estrella Sadhala. next corner from Caribe tours bus station so you can use this bus co. to get from Mao to Santiago.