Be grateful you can encounter it at all.
Niantic typically themes Pokémon Go Fest around one core mechanic or Pokémon, with a few wrinkles thrown in to keep things fresh. And with Go Fest 2022 the Mythical Pokémon Shaymin will be at the center of attention as it makes its Pokémon Go debut.
Just like with previous events, Go Fest 2022 will be the only method to obtain Shaymin and it will be exclusively available to players who purchase an event ticket.
Starting today, players can purchase their tickets for Go Fest 2022 from the in-game shop, which will cost $14.99 and give them access to the event on Saturday, June 4, and Sunday, June 5. Ticketed players will gain access to a customizable Special Research story on June 4 that will include a guaranteed encounter with Land Forme Shaymin.
You will need to complete all of the research tasks up to a certain point to earn that encounter, but once you do, the spawn will be available once you claim your reward. And, because this is a research reward, Shaymin wont run away, which means you are guaranteed to catch it as long as you have enough Poké Balls.
Sky Forme Shaymin has not been confirmed for the event yet, but it is likely that this Shaymin will be the only one available for quite some time regardless.