You can't change a Pokemon's regular ability to their hidden ability in any way. Ability Capsules can't even accomplish this.
In the past, there was a dream world game for generation 5 where you could catch Pokemon on the global link website and send them to your game with their HA, but that was removed after X/Y were released. Pokemon obtained in Dream Radar have their hidden abilities.
>Some overworld Pokémon in Pokémon Black and White have their Hidden Ability:
The five Darmanitan in the Desert Resort.
The Musharna in the Dreamyard on Fridays.
Any Pokémon found in Pokémon Black 2 and White 2's Hidden Grottos have their Hidden Ability. In addition, the following Pokémon will have their Hidden Ability:
On Mondays, a male Jellicent at Undella BayB2 or a Braviary on Route 4W2.
On Thursdays, a Mandibuzz on Route 4B2 or a female Jellicent at Undella BayW2.
A Deerling given as a gift on Route 6
Yancy/Curtis will trade the player a specific Pokémon with a hidden ability after entering the Hall of Fame and riding the ferris wheel with them.
Pokemon from friend safaris have hidden abilities.
Some Pokemon event distributions have Pokemon with their hidden abilities.
Pokemon in Horde battles can have their HA
The dexnav in ORAS can find Pokemon with HA's, you'll know if a shows a question mark.
So you can only get hidden ability Pokemon from friend safaries and events and Dexnav, unless there ends up being another alternate way in the future.
You can also breed Pokemon to give the baby the HA.
Here is a list of Pokemon with released Hidden Abilities
Sources: Bulbapedia Dexnav info| Bulbapedia HA info