Blue can be found at Cinnabar Island. You have to defeat the other 7 Kanto gym leaders before you are able to battle him.
Cinnabar Island.
go to cinibar iland and go by the Pokemon center and you will see a gey. talk to him he will leave. then fly to viridian city. GOOD LUCK!
The Viridian Forest. They're hard to find.
In the original Silver game, the gym leader was Blue and you would find him at Cinnabar island. After meeting him there, you can go back to the gym and fight him.
In Pokemon Heartgold or gold and soulsilver or silver you can find it in viridian forest.
Firstly, have to defeat the 7th gym leader. Then you go talk to the trainer next to the Pokemon center on Cinnabar Island. He is the 8th gym leader of Kanto, Gary. Gary is in Viridian City.
His name is Blue, and he is on Cinnabar Island. Show him the other 7 Kanto Badges and he will go to the Viridian City gym. Then, go to Viridian City and battle him at that gym.
I believe after you beat the viridian city gym leader he disappears.
Go to viridian forest and look around a pikachu is likely to show up
in viridian city
In the goldenrod gym.
viridian forest or the pokewalker resort route