Mr. Mime may be a terrifying amalgamation of man and Pokémon, but you'll still want him to fill out your Pokédex. While Galarian Mr. Mine can be found in the wild with Sword and Shield, Cantonese Mime can only be obtained through an exchange with an NPC.
Kantonian Mr. Mime won't stand out in a battle, but if you want to get your hands on all the Pokémon and variations of the game, then you'll want to know how to add him to your collection.
The first thing you will need is Obstagoon. Many special Pokémon can be obtained through exchanges with NPCs, and that's exactly how you get Kantonian Mr. Mime. To get an Obstagoon, go to Route 2, then use your Rotom bike with the Surf upgrade to travel on the water. You can regularly find an Obstagoon in the grass in that area.
Once you have your Obstagoon, go to Spikemuth. Fly to Route 9, then cycle to the Challenge Gym in the city center. You'll find a grunt from Team Yell sitting in a booth in the left corner. Talk to him and he will offer you a Mr. Mime if you give him Obstagoon. Accept the trade to get your Kantoniam, Mr. Mime.
This is the only Kantonian Mr. Mime available in the game; you can't breed it with other Pokémon to get more, as any Mr. Mimes that spawns from eggs will be the Galarian version.
Now that you've added Kantonian Mr. Mime to your Pokémon collection, you're even closer to getting them all.