If this was a game where updates were done automatically (Like all the the new games do), then Ame would do those changes retroactivly and the people that have/had a Gyarados, wouldn't have it anymore. Sadly, that's not how the game works, so anyone with an older episode can get whatever pokémon was available before it was axe'd. Welp...
Sorry, the God-Janitor-Sweeper-OPAF Gyarados lord is not available anymore, and I'm not even sure if the event will be over in episode 16.
Should you need help with a new strategy, or a pokémon that could fit in your team like Gyarados, you can always head to the Team Showcase section and ask for help there~