All of these are gotten in Circhester. Go to your Pokemon Center, go right towards the hotel and go in on the left. After the defined conditions are fulfilled, you speak to the corresponding person to get the Charm you want.

Catching Charm - boosts the rate of a critical capture
Go to the second floor, and into the second room on the left. Speak with the doctor there.

Oval Charm - Makes it more likely for Pokemon to lay an Egg at the nursery if they're compatible
First, become the Champion of the Pokemon League. Go to the second floor, and into the first room on the left. Battle the cop there.

Shiny Charm - triples the frequency at which Shiny Pokemon appear
First, capture all 400 Pokemon in the Galarian Pokedex. Speak with the same doctor who gave you the Catching Charm.