In Pokémon Sword and Shield
Fortunately, for players who have previously played either Pokémon Let’s Go Eevee or Let’s Go Pikachu on their Nintendo Switch, there’s an easy way to get your hands on a special Gigantamax version of one of these Pokémon.
The Pokémon you get depends on the game for which you have a save file, so those with a file for Let’s Go Eevee will receive a Gigantamax Eevee while those with a file for Let’s Go Pikachu will get—you guessed it—a Gigantamax Pikachu.
Now, onto how to get them. Like the Hi-Tech Earbuds item in Sword and Shield, getting your hands on these Pokémon is simply a matter of finding and talking to the correct NPCs.