There are only three methods that can give a Pokemon their hidden ability. And one is discontinued... and the other two are rather restrictive.
- In the Dream World (which now no longer exists, Lol)
- The Pokemon that appear in hordes have a chance of inheriting their hidden ability. (Few Pokemon appear in hordes, and otherwise at quite a low level)
- Pokemon in the Friend Safari have their hidden ability. (The Friend Safari only shows Pokemon of certain types (Grass, Fire, Ghost, and possibly even just Ditto) and is only accessible if you have traded friend codes with another person. So, a very restrictive place)
So, you may not have the best time finding a Pokemon with Hidden Abilities.
Unless it's any bit helpful, the Torchic + Blazikenite event is still ongoing, and it has it's hidden ability Speed Boost. :D
Hope I helped. :)