This is the easiest way to get Pokémon with hidden abilities in X and Y. If you and your friend have been online together at least once, then the Pokémon that appear in the Friend Safari can have hidden abilities. Use a Pokémon with the ability Trace to make it easier to find the Pokémon with hidden abilities.
In X and Y, there is a small chance that a Pokémon in the horde will have its hidden ability. It will be more difficult and time consuming hunting them out though.
To pass down hidden abilities, one of the parents need to have the hidden ability. I believe females have a higher chance off passing it down, but I'm not sure.
Hope I helped!
Here is a page on breeding if you need it.
Edit: The Dream World was a way to obtain Pokémon with their hidden abilities in Black/White and Black/White 2, but unfortunately is no longer available.
According to the Pokémon Global Link website, the Dream World closed on January 14, 2014, alongside all other services for Generation V games.
For this reason I will not go in to detail explaining it, if you really want to know please look at the link above.