First you have to beat the Elite four then you get to go to Kanto region, and the first city with a gym leader present should be Pewter.
its in the same place it is in the normal kanto region,but you cant get there until you defeat the easy elite four
what you have to do is use the digletts cave all the way from Vermillion City, but there is a Snorlax in the way. Check on your radio if you have the PokeFlute channel, its all the way at the top. If you don't have it, I'm pretty sure you have not fixed the radio tower incident. Not the Goldenrod one, the one involving the Power Plant. Then I'm 100% you should be able to reach Pewter City.
You have to go to Lavender Town then go into the Radio Tower. There is an old man standing by the elevator and he gives you the poke Flute. Go to the snorlax in Vermilion City and then go to your Pokegear and use the pokeflute. You should finally exit your Pokegear and snorlax attacks. Go through Diglett's cave and you're there. (You need to cut in order to get through).
You have to wake up the sleeping snorlax in front of digletts cave, using the Kanto radio. Then use digletts cave to get to pewter city
Pewter City
You can fly there or go west.
At the top of pewter city in the kanto region
talk to the man on the platform in pewter city
Its in Kanto to the right of Pewter city.
go down at pewter city
to pewter city
go to the museum in pewter city
After you get the silver wing from the old man in pewter city
Go north from Viridian City or south from Pewter City.
In kanto, south of pewter city, north of viridian city.
In Pewter City. There is an old man on a hill that gives you a silverwing