Want Charmander ASAP? How to Grab Bulbasaur, Charmander, or Squirtle in Pokémon Legends: Z-A

If you want a Kanto starter in Pokémon Legends: Z-A, you can get one during a specific side mission — and the process is straightforward once you know the steps.
How to get Bulbasaur, Charmander, and Squirtle in Pokémon Legends: Z-A
To receive your first Kanto starter you must reach rank W with Team MZ. Then, the following day you will be sent on an errand that ends with a battle against a fellow Team MZ member. After that battle, heal at a Pokécenter and you will get a call on your Rotom phone from Mable. The side mission “A Call from Mable” becomes available at that point. Finally, go to the Pokémon Research Lab and head to Mable’s office; the three Kanto starters will be waiting there for you. 
Where they appear
The Kanto starters — Bulbasaur, Charmander, and Squirtle — appear together in Mable’s office at the Pokémon Research Lab during the “A Call from Mable” side mission. You do not encounter them in the wild at that moment; they are presented as selectable NPC Pokémon inside the lab.
How to pick one
Follow these concrete steps:
- Reach rank W with Team MZ.
- Complete the next-day errand and finish the battle against the Team MZ member.
- Heal your party at a Pokécenter so the Rotom phone call from Mable triggers.
- Accept the side mission “A Call from Mable”, then visit the Pokémon Research Lab.
- Talk to Mable in her office and choose one of the three Kanto starters — Bulbasaur, Charmander, or Squirtle — to add to your team.

Once you pick one, that Pokémon is added directly to your party.
Getting the other two Kanto starters
The remaining two Kanto starters are not given during the same mission. Instead, you can obtain them in the post-game. Alternatively, you can get them via trading with another player who has those starters. Note that there is no breeding in this game, so trading may be the only way to get extras before post-game content becomes available.