Lovely Grooming raises a Pokémon's friendship by 30. This amount is unaffected by Soothe Bell.
Lovely Grooming can be received from the PokéGroomer, who is located in the Beachside Resort and Casino restaurant area. Lovely Grooming is at the charge of 
3000. Due to his "busy schedule", he can only groom a single Pokemon once per day, so make it count.