Buses running between the nearby larger cities (Phitsanulok, Khon Kaen, Phetchabun) usually (but not always) stop at Lom Sak's bus station. There are also buses direct from Bangkok's Mo Chit bus station. If you find yourself on a bus heading north to more remote towns, you may pass through central Lom Sak itself after stopping at the bus station. Always check first to make sure!