Haxorus itself can't be found in the wild, only it's evolutions can.
An Axew can be found at Level 14 in the Connecting Cave. Or, an Axew can be found in hordes, but it can only be found at Level 7, but you can always have luck in getting it's hidden ability like that. xD
Also, you can find Fraxure in the Friend Safari, at Level 30, which might be a better option since at least you can only wait 18 levels rather than flippin' double that. xD
Hope I helped. :)
Source: Serebii's Pokedex Entries on the three evos.