Shaymin is a Grass-type Mythical Pokemon, and, like most Mythicals in Pokemon GO, players can only get one by completing a specific Special Research Story.
The only way to catch Shaymin in Pokemon GO is by completing the Grass and Gratitude Special Research Story. An encounter with Land Forme Shaymin is a reward for finishing step 6 of this Research.
However, there is currently no way to catch Sky Forme Shaymin in Pokemon GO.
The Grass and Gratitude Special Research Story was added during the 2023 Sustainability Week event. This is the first time that every Pokemon GO player could catch Shaymin without buying a Reserach Ticket.
Previously, both Shaymin Formes were available to catch as part of the 2022 Pokemon GO Fest event. However, only players who purchased tickets for limited-time Research could catch them.
This meant that both Land Forme and Sky Forme Shaymin were locked behind a paywall when they first debuted.

When Will Sky Forme Shaymin Be Available to Catch?
We expect Sky Forme Shaymin to be the next Mythical Pokemon to get a Special Research Story in Summer 2023.
This is because Land Forme Shaymin became available for every Pokemon GO player in April 2023, and, judging by the previous release pattern, Sky Forme Shaymin should follow soon after.
Sky Forme Shaymin made its debut in August 2022 as part of the ticketed Research for the 2022 GO Fest Finale, two months after Land Forme Shaymin.
While you’re waiting for Sky Forme Shaymin to come to Pokemon GO, there are plenty more Mythical Pokemon to catch. Here’s the list of every Mythical Pokemon in Pokemon GO so you can find out which ones are missing from your Pokedex!

If you want to easily catch another Mythical Pokemon, there’s one which is pretty easy to get. Find out how to catch Meltan in Pokemon GO if you don’t have one already!