you need to beat the 4th gym and you get it from warden the old man in fuchsia city to the right of the Pokemon Center by giving him the gold teeth from the safari zone
Rock tunnel is on route 7. Be sure you have the HM Flash handy and have beaten the Vermilion gym.
defeat silph co then the rockets wont block u
i am pretty sure it's strength.
I believe that is after you've beaten the 4th Gym in Volcanoridge Town.
you fly 2 pallet town and surf south then u have to get through the Pokemon mansion
Once you have beaten the first Gym,in Pewter City, Professor Oaks Aid will give them to you as you leave towards Mt Moon.
In his gym
the 5th gym is saffron gym with sabrina!
If you have beaten Mauville Gym and have gotten HM ROCK SMASH, go to RUSTURF TUNNEL and clear out the rocks. The digger will grant you HM STRENGTH.
You need to obtain a certain gym badge. (Not sure which one) And then you can use it. If you do have the gym badge, go up to the boulder and press a. Or go onto Pokemon and select the Pokemon that knows strentgth and go down and select strength. Hope this helps! Posted by Rebecca Castle
Viridian city the first place you go to at the beginning of the game.The 8th and final gym is in Viridian City, the first city after the hometown, although cannot be challenged until after all other gyms are beaten.
Misty