Tickets to #PokemonGOFest are now sold out. Stay tuned for how to participate in Pokémon GO Fest together with Trainers around the world.— Pokémon GO (@PokemonGoApp) June 19, 2017
You may not be able to get a ticket anymore through official means, but you can always hit up eBay for a ticket. The bad news is, tickets are being sold for $400 and higher, which is absolutely insane! Thanks to AlienboyVA for the heads up!