He won't be in viridian at first he will be at cinnibar island if you talk to him he will go to the gym in viridian city go to viridian city to battle him.
Blue
Viridian Forrest in the kanto region
after you defeat Blue, in viridian city
He is the gym leader Viridian city
Route 2, north of Viridian City, south of Pewter City, where Viridian Forest was in Red and Blue.
Viridian City, the second town you are ever in
Blue is the Viridian City Gym Leader (Badge #16)
Blue is the viridian gym leader and red is on top of mt silver once you beat all the kanto gyms
Red is at the top of Mt. Silver. Blue is the Viridian City Gym Leader.
You can catch them in Viridian Forest as well as the Power Plant
Defeat the viridian city gym leader Blue.
you don't first you talk to blue at cinnabar. then you go to Viridian and battle him at the gym then you go battle red at mt. silver.