Professor Elm will give you HM Rock Climb after the 16 badge.
I think after you have collected all 16 badges you can talk to prof. elm and he will give it you.
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you get it AFTER you beat blue
you get it from oak after beating blue
its on cinnabar island. you have to have rock climb though. go to the Pokemon centre and go up to where blue is/used to be and use rock climb, then take the nearest rock climb to you and roll from there (:
Beat Blue and go to Professor Oak in Pallet Town. He gives HM 08- Rock Climb to you.
rock climb