First you have to go to Fushia city with Pikachu and go to the pokemon center. When you're by the center, jump off the hedge and don't let Pikachu follow you. Wait until Pikachu starts walking in place and then start walking away. If you do it right should see Pikachu floating behind you

Get Bulbasaur

After you get Squirtle, go to Cerulean city, and in one of the houses there is a lady, who has Pokemon next to her. Talk to her and she will ask you a question. Choose the top answer and she will ask you another question. Choose the top answer again and you get Bulbasaur!

Get Charmander

There are several ways to snag Charmander. On way is to travel to Ceruleon City, and talk with the man on the other side of Nugget Bridge. The other way is to beat SS. St. Anne to port and speak to Officer Jenny.

Get Squirtle

After getting off the S.S. Anne, and getting the Thunderbadge from the gymleader, Lt. Surge, then you can get Squirtle from Officer Jenny in the middle of town.

At the start of the game Gary will receive an Eevee. Determining its evolution depends on your fighting performance. In the lab fight if you lose and skip or lose the Viridian battle, Gary will get Vaporeon. If you win the lab battle and skip or lose the battle in Viridian, Gary will have Flareon. If you win both the lab fight and the Viridian battle then Gary will have Jolteon.