On route 11, you can find nidorans in a horde encounter. Pokemon in a horde encounter have a chance of having thier hidden abilities. So if you search around for awhile, you will eventually find a hustle nidoran. this may take awhile, but its the only way.
EDIT--- you are playing x, so the encounters you find them in will have 4 boy and 1 girl nidoran. I assume this is good for you because you said you wanted a nidoking.
