Yea, the new breeding mechanics allow you to breed a HA down from a male, so it's possible to get one from someone who did so, they just weren't too common to begin with.
Damp is a really limited use ability. The stuff it protects against hardly comes up, even in just a normal playthrough. I'm really bummed he didn't get something more useful like Water Absorb or even Hydration, since Mudkip is my favorite starter.
Good luck finding one, regardless!