Outside of Nacrene City,towards Pinwheel Forest.On the way there,a nurse will battle you.Talk to her and you will get the TM after you battle her.
In this game, rock smash is not an HM, it is a TM.
Rock Smash is not a HM, it's a TM. You can get it from a Battle Girl outside Pinwheel Forest
Rock Smash is now a TM found in the outer part of Pinwheel Forest. A girl next to a sign will give it you.
You can get the TM Rock Smash from a lady near the Poké Center in Ambrette Town.
You use the Rock Smash TM
A wide variety of Pokemon can use Rock Smash. Most Fighting, Rock and Ground type Pokemon can learn the move Rock Smash from the TM or HM depending on the Pokemon version.
Well in Pokemon black and white its no longer a HM its now just a TM if its not working in battle your game is messed up
Strangely, Rock Smash is not a HM. It is a TM. The girl at the entrance of Pinwheel Forest gives it to you.
You can get the TM Rock Smash from a lady near the Poké Center in Ambrette Town.
You get it at Ambrette Town in the laboratory. And it's not an HM; it's TM94. Rock Smash went from being an HM to a TM in the 5th generation games (Black/White/Black 2/White 2).
In Mauville City, there is a house south of the Bike Shop. In the house live a person called the "Rock Master". Talk to him, and he will give you TM 06, Rock Smash.
You obtain Rock Smash from Wally's uncle in Mauville City after defeating Wally in front of the Gym.