Beat all 16 gyms and prof. Oak will give it to you.
Once you get all 16 badges Professor Oak calls you then go to his lab in Pallet town
if poke man want to learn rock climbing. He must be join some training or buy Climbing Gear For Beginner.buy it.
After you get all 16 badges oak kalls you and he gives you it
AFTER ALL 16 BADGES ARE YOURS THEN OAK CALLS GO TO HIS LAB AND HE WILL GIVE IT TO YOU if you went to his lab before he said "come back after you have all 16 badges and ill give you a surprise"
^^^^ oh my god after getting all sixteen badges??? Gawd you got to be kiddin me.. That's so long!
Beat all gyms then prof oak will call then go to where he is go north from cherrygrove city no't the first house but the second
After you get all 16 badges