Mahogany City, until you catch or faint the red gyrados in the lake of rage.
You have to defeat the gym leader in that town.
You can't get past that guy until you go to the Lake of Rage and catch/defeat the Red Gyarados. After that he'll go away.
go to the radio tower in goldenrod city an defeat all the team rocket dudes you will get the silver wing then go to mahogany town and go -> passed the guy that sells rage candy bars and your in blackthorn city.
it is easy just kill the ice gym kill or grt the red dragon and pass
you have to go help the light house Pokemon in Olivine city, idk if you have to do this part, but i got the 5th 6th and 7th before i went again and he had moved :d
If it is the guy who wants you to buy a rage candy bar, buy it or go away for a bit and never get a chance to buy it again. If there is some guy blocking the cave entrance you have to go to the Lake of Rage.
a guy gives it to you at mahogany town
btw I'm stuck as well and i can't get the fat guy out the way or even find a red gyrados you can catch the red gyarados up the top of lage rage
you have to give the ampharos at the light house in olivine city medicine from cianwood city. once you complete that he should let you pass
go to the guy that sells rage candy
you give it to a guy underground in kanto.
you have to go to the guy blocking you from blackthorn city