not possible
you cannot catch celebi in Pokemon leafgreen. you can only get it through cheat codes or trading.
you cant catch celebi in the gba games except with a game shark cheat system
cheat.
either use action replay or event or catch wild in victory road after you get mew.
You can't catch celebi in pokemon white.
you can not catch celebi in Pokemon platinum
Nintendo events
you can trade it
It was only possible by going to a Nintendo event. You can get one now by trading or using codes.
No you cannot catch Celebi in Pokemon Emerald.
you can not catch him
The only legitimate way to obtain Celebi and Mew is through a Nintendo event. In FireRed and LeafGreen you will need an event-only item to travel to the last two islands where you can catch those Pokemon