To get a Gigantamax Pokémon in Pokémon Go, you first need to defeat it in a Max Battle at a Power Spot. Afterwards, you'll have a limited number of Premier Balls to catch the Gigantamax Pokémon.

That said, there is plenty of opportunity to recruit powerful Pokemon such as Machamp ex or Marowak ex ... Pokemon with a benched Pokemon. This can get annoying for the opponent very quickly.