https://www.gamespot.com/articles/pokemon-go-legendary-week-offers-a-chance-to-catch/1100-6456967/

With the second Pokemon Go Community Day approaching, developer Niantic has announced another, unrelated event that is now underway. And if you missed out on the opportunity to catch two of the previous Legendary Pokemon that were available in the game, you're in luck, as they're back for a limited time.