You cannot capture wild Pokémon with their HA naturally.
Instead, you will either have to look in Friend Safaris (XY) or DexNav chain (ORAS).
Friend Safari: There is a good chance of encountering an HA Pokémon in a Friend Safari. It is not guaranteed, but there is a decent chance.
DexNav Enounters: The more you encounter a certain species of Pokémon, the higher chance there is of that Pokémon having beneficial features. These features include Egg Moves, IVs, and Hidden Abilities. The more you encounter a Pokémon, the higher chance there is of it having an HA.
Friend Safari Pokémon