Hidden Ability Shelgon is only available in the Friend Safari, and is generally quite hard to find if you are aware of the Friend Safari mechanics.
Hidden Ability Bagon is only achievable by breeding a Hidden Ability Shelgon (both genders can breed down hidden abilities to the offspring now, I believe)
Hope I helped. :)
Source: http://www.serebii.net/pokedex-xy/372.shtml and Experience