To help shiny hunters and Pokémon trainers alike, members of the Pokémon Sword and Shield community have set up a specific Trading Hotline for Foreign Dittos in games.
Trainers can go online using YComms and using the Link Code 4448, which will hopefully link them with others around the world who are looking to trade Ditoos from different regions.
The reason behind the need for trainers to own a foreign Ditto comes from the Masuade Shiny Hunting method. In short, by breeding a Pokémon from two different regions, the chances of getting a Shiny Pokémon from those eggs increases dramatically.
So if you were to breed an English Scorbunny from the U.S. or U.K. with a Japanese Ditto, the chances of getting a Shiny Scorbunny fall to around one in 500, instead of one in 4,000.
While there is no guarantee of getting a Ditto from a different territory, you might as well still try your luck. Some people over on Reddit have confirmed it was working, and if enough people get behind the movement, it could be quite successful.