Since Litleo / Pyroar are unavailable in ORAS, you will have to trade with someone if you wish to obtain one (e.g. XY).
In X/Y, you will only be able to get Hidden Ability Pokemon in the Friend Safari so you will need to find someone with a Litleo / Pyroar in their Safari. You can use the Trace ability (Ralts, Kirlia, Gardevoir) to shorten the amount of time needed to find a Pokemon with a Hidden Ability.
Other than the Friend Safari, you will just need to find someone with a Hidden Ability Litleo / Pyroar.
Hope I helped!