on route 217 outside the mans house you will see a pokeball. pick it up and you have HM08
HM08 is only in ruby, sapphire and emerald.
You find HM08 Waterfall on BF4 of the Cave of Origin
D.I.V.E
There is no HM08 in Pokemon Crystal. Pokemon Crystal has only 7 HMs that are available to use.
You do not need HM08 to reach Cinnibar Island. You do, however, need HM08 to search Cinnibar Island. Without HM08, all you can do is use the Pokemon Center.
HM08 Rock Climb is given to you by Prof. Oak once you have all 16 badges.
Rock Climb
You go to Steven's house in Mossdeep city. He's northwest of the Pokemon Center. When you enter, he'll give you HM08. HM08 (Dive) is exclusive to Pokemon Ruby and Sapphire and is obtainable in Mossdeep City from Steven who resides there. Steven
beat the 8th gym and then go up and there is a person from hoen and also gym leader will give it to you
There are only 7 HMs.
after you defeat trainer blue, the last gym leader in kanto, talk to prof. oak. he will give it to you
Jasmine is located in the north of Sunyshore City. She gives you HM08 Waterfall after you acquire the eighth gym badge from Volkner.