The Pokemon Company cooperates with game stores around the world to provide players with the opportunity to acquire Shiny Zacian and Shiny Zamazenta in the Pokemon Sword and Shield. PKMBuy is a safe store if you want to buy 6IV Shiny Ditto. The event is currently underway, but this promotion will vary depending on where you live.

Currently, if you live in the United States or Canada, Shiny Zacian will be available from October 22 to November 11, and Shiny Zamadenta will be available from November 12 to 27. Globally, players can only get Shiny Zacian in Pokemon Shield, get Shiny Zamazenta in Pokemon Sword. Swapping the cover legendaries to make sure everyone can have it in their PokéDex at the same time. 
 
If you are in another area and want to receive your Shiny Zacian or Shiny ZaMazenta, or you have both Sword and Shield, then the method to receive your Shiny Zacian and Shiny ZaMazenta is as follows:

United Kingdom – GAME: In-store and online

Germany, Austria, Switzerland – GameStop: In-store only

Ireland – GameStop: In-store and online

Spain – GAME: In-store and online or FNAC: In-store only

France – Micromania: In-store and online

Italy – GameStop: Online

Belgium and the Netherlands – GameMania: In-store and online

Denmark – Nintendopusheren: In-store, NØRDCON: Oct. 23 and 24 only, or Pro shop: In-store and online

Sweden, Norway, and Finland – Pro shop: In-store and online

South Africa – Nintendo Distributor Email

Japan – All videogame retailers: Show clerks your Nintendo Switch Home Menu with a copy of Sword or Shield present 

Malaysia, Philippines, Thailand, and Singapore – Various retailers: In-store only
Hong Kong – 1O1O Center or CSL Mobile: In-store only

So far, this limited promotional distribution is the only way players can legally obtain Shiny Zacian and Shiny Zamadenta, although they may be distributed multiple times in the future. If you are playing Pokemon Sword and Shield and need other shinies, you can Buy 6IV Shiny Ditto on PKMBuy for a low price.