Since you are attempting to get a pokémon with a Hidden Ability (HA) in X and Y, there is only one way to get pokémon with their HA's. That is Friend Safari, which is unlocked post-game. Friend Safari is a place where you can find specific pokémon, which are assigned to every single trainer. (Note that you must have at least one friend registered into you 3DS.) Some of the pokémon you catch at the Friend Safari will have their Hidden Abilities. When I went into my friend's Safari, I found a Frogadier with Protean. Now here's the next part. You can breed your new Pokemon to get the offspring. If I am breeding a Male Ivysaur that has Overgrow, with a female Chloryphyl Ivysaur, the offspring will have a 80% chance of having the hidden ability. Basically, the female Pokemon has to have the HA. The story is different with a Male Chlorophyl Ivysaur bred with a Ditto. The offspring will have a 20% chance of having the HA.
Source(s): My own experience