If you want to go shiny hunting at all costs, it's better to get the Shiny Charm back in order to maximize your chances of finding some!
Where to find the Shiny Charm?
- Complete your Pokédex 100%
Once this mission is successful, you must go to Circhester. Go back to the Iona Hotel (the one on the left of the central fountain).
In the second room on the left, you will find the director of the game. If you have already come, he will have given you the Catching Charm to help you with Critical Captures. But once your Pokédex is complete, it will give you the Shiny Charm!
To complete your Pokédex in its entirety, don't be afraid to trade with friends, or around the world with surprise trades.