Only two ways to get Hidden Abilities and one of them is ruled out.
Hordes, you can search for one in a hoard which the easiest place will be the cave next to Route 7. For quick hoard encounter have a Pokemon with Sweet Scent
Friend Safari, this is the one ruled out because you cannot catch a Zubat or it's evoultinary with their hidden ability.
An alternative is to check the GTS though that isn't always relieable.