Originally Posted by MagmarMan
Bulbasaur is available in one of the houses in Cerulean City. Charmander is available by talking to the kid directly above Nugget Bridge. Squirtle is available in Vermillean (spelling) after beating Lt. Surge.
Well, Squirtle is the easiest to get since you just need to beat Lt. Surge.
And the hardest is Bulbasaur. I never knew he exact details and requirements on how to get it but I always got it with pure luck. :p