Where To Get Rock Smash In Pokemon Light Platinum?

I am playing the game now, I have beaten the 5th gym leader and I am about to face the 6th.

You get rocksmash near the start of the game in seanport city, go in to each house, and there should be a guy with glasses in one of then, talk to him and he will give you the HM06 rocksmash.
I hope I helped!