Is there a way to obtain Shiny Mewtwo in Let's Go without repeatedly reloading save files?

In Let’s Go, it seems that, as far as I know, Mewtwo is the only Pokémon that does not respawn (the legendary birds can be found in the wild).

Since Mewtwo does not respawn, is there any way to obtain Shiny Mewtwo in Let’s Go without reloading a save file hundreds/thousands of times, or is reloading a save file hundreds/thousands of times the only way to obtain it?

Note: In the future, it will be possible to transfer a Shiny Mewtwo from Pokémon Go to Let’s Go. I’m specifically asking this question in the context of Let’s Go itself.