Farfetch'd - found by trading a spearow for it in Vermillion City.
Mr. Mime - found by trading an Abra for it at the end of Diglett's Tunnel
Eevee - found at the top of the mansion in Celedon City. To get it
you must go to the back of the mansion and enter there.
Flareon, Jolteon, Vaporeon - use either a water stone,
thunder stone, or fire stone on Eevee to turn it into one of the three.
Hitmonlee, Hitmonchan - defeat the gym in Saffron city
beside Serina's Gym and choose between a Hitmonlee or a Hitmonchan.
Zapdos - found at the end of the power plant.
Articuno - found in the cave on Seafoam Island. You must stop the
current to be able to swim to it.
Moltres - found on Victory Road on the way to the Elite Four.
Mewtwo - found in the cave that is around Cerilion City (with Misty).
Swim to the island where the guy was standing and enter the cave. You
must beat the Elite Four before you can enter. *Warning* the enemies in
this cave are far more dangerous then any other that you have encountered
in the game. Bring some escape ropes because once you get to and catch
Mewtwo you will be too weak to make the trip back!*
Porygon - Trade 6500 coins for it in the blue version at the casino or
pay 9999 coins for it in the red version.
Mew - All rumors about getting mew are FALSE! You can not push
a truck to get him. The only way to get him is gameshark/gamegenie.
Lickitung - Trade a Slowbro for it in the building west of Fushia.
Lapras - After defeating Gary in the Team Rocket head quarters talk
to the guy beside you and he will give you a Lapras.