Not every Pokémon in Pokémon Go can be Shiny, and even those which can can still be pretty difficult to track down. Outside of an event, your best chance at finding Shiny Pokémon is to click on every single Pokémon you encounter whose species have the potential to be Shiny. Here's which Pokémon you should be Shiny checking.
C.J. is a beaver who shows up periodically in Animal Crossing: New Horizons. He'll randomly make visits to your island, but he'll also host various fishing competitions throughout the year where you can earn a ton of Bells and sweet Fish Swag.