Nincada is a fantastic Pokemon to use these moves on. Not only can it learn Flash and Rock Smash, but also Cut, Dig, and Secret Power which are all moves that are required later on.
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HM06 Rock Smash
no Pokemon can learn rock smash by leveling up you have to get the hm.
Victory Road (use rock smash)
Cut, Strength, Flash and Rock Smash.
Well.... I guess mew, but you need an event. If that doesn't work, kyogre can learn surf, waterfall, dive, rock smash, strength, and maybe flash.