There is a key in Pokemon Mansion (Searching for Mew there on LeafGreen. I know a glitch to get Mew before Misty on Pokemon Yellow without GameShark!) You have to hit the switch on every Statue (At least in LeafGreen. I beat it!) and that Item You NEED to get is the gym's key. Get it. Go to the gym. Use it. Your in.
Pokeglitch20
After beating the 6th gym, enter the baggage building at the airport, you will be flown across to the other side of the map. There's a few locations in between, but your goal is Opelucid City.
The 7th gym leader in Pokemon yellow is in Cinnebar Island, which is south of Pallet Town. You need a Pokemon with Surf to get there.
Yea there is the island with the 7th gym on it is an island.
The 7th gym leader is Blaine. He the gym leader of Cinnabar Island gym. He uses Fire type Pokemon and he will give you the TM that contains Fire Blast when you defeat him.
there is a key in the Pokemon mansion... you need it to get into the gym... search the Pokemon mansion thoroughly
Beat team rocket at Mt moon, Pokemon tower, rocket game corner and silph co. Then get the 7th badge now you can go into the viridian city gym to get the last badge.
In the cinnibar island gym.
beat the 8th gym
in the bottom of the Pokemon mansion
in snowpoint city
In 7th gym
Giovanni
Fuchsia city.