From Bulbapedia, the community-driven Pokémon encyclopedia.
This is a list of Pokémon obtainable from events found in the Generation I Pokémon games. These specific instances of Pokémon can only be obtained once per game; however, some may also be obtained in other ways as well.
A salesman in Route 4's Pokémon Center will offer a Magikarp to the player for 500.
There are two set encounters with Snorlax accessible via the Poké Flute; one on Route 12 and one on Route 16. The player must capture or defeat at least one of them to proceed to Fuchsia City.
Hitmonlee and Hitmonchan
Kiyo, the master of the Fighting Dojo in Saffron City, will reward the player with their choice of either Hitmonlee or Hitmonchan after defeating him.
After defeating Blue during Team Rocket's invasion of Silph Co., an onlooking Silph employee will entrust the player with a Lapras.
Omanyte and Kabuto
The Helix and Dome Fossils are found at the end of Mt. Moon, but the player may only choose one to keep. The player may revive the Fossil in the Pokémon Lab on Cinnabar Island.
The Old Amber is located in the secret part of the Pewter Museum of Science, which can only be accessed with HM01 (Cut). The player may revive the Fossil in the Pokémon Lab on Cinnabar Island.
Articuno is found within the depths of the Seafoam Islands.
Zapdos is found inside the abandoned Power Plant.
Moltres can be found in Victory Road.
Mewtwo is found within the depths of Cerulean Cave, accessible only to powerful Trainers who have entered the Hall of Fame.
Pokémon Red and Blue (English) / Pokémon Red, Green, and Blue (Japanese)
Professor Oak gives the player a choice of Bulbasaur, Charmander, or Squirtle as starter Pokémon.
A Poké Ball containing Eevee can be found on the roof floor of Celadon Mansion in Celadon City.
Pikachu will be caught and given to the player by Professor Oak.
A Poké Ball containing Eevee can be found on the roof floor of Celadon Mansion in Celadon City. Despite being the same level, its moves differ from Eevee acquired in the earlier Generation I games due to its level-up learnset being updated in Yellow Version.
Bulbasaur will be given to the player by a girl in Cerulean City if the player's starter Pikachu has high enough friendship.
A boy north of Route 24 will give the player a Charmander.
An Officer Jenny in Vermilion City will give the player a Squirtle after defeating Lt. Surge.