On the local level, tournaments are run by Pokémon Professors. These are people who love Pokémon and share that love with their community. Pokémon Professors may be staff of a local game store, or they may be volunteers who run events at game stores or other venues.
If you have checked the Event Locator and don’t see any events for a game you play, but do see stores running events for other games, reach out using the contact information for those stores and see if they would be interested in running events for the game you play!
If a store is interested in hosting events for your game, but doesn’t feel knowledgeable enough to run a tournament, consider becoming a Pokémon Professor yourself! After passing the Organizer exam, you can run casual tournaments – by being involved with your local store’s League, you can become a League Assistant and start running Championship Series events like League Challenges and League Cups.