once again it is a simply thing even for noob just keep walking in Pokemon there are no short cuts when it comes to gyms if you skip one your screwed later on.
hm01 cut
keep walking or fly to the second closest city to you.
The key to the gym
The fifth Gym Leader in Pokemon LeafGreen is Koga, the leader of Fuschia City's Gym. He specializes in Poison-type Pokemon and hands out the Soul Badge.
the 5th gym is saffron gym with sabrina!
Yes, if you get the Gym Badges.
Misty
Sabrina's gym in saffron city
there is a key in the Pokemon mansion... you need it to get into the gym... search the Pokemon mansion thoroughly
I think the gym in fuschia city
viridian city
there isn't one