To get HM 05 Flash, first go through Diglett Cave in Vermillion City ... teaching it to a replaceable Pokemon who's not part of your main team. Before Rock Tunnel, your choice is actually rather ...

Oreburgh Gate is a tunnel with ... As you enter the cave, a man will immediately intercept you. He'll talk with you and give you HM06 in DP / TM98 in BDSP - both are Rock Smash.