Not counting hidden grottos.If you can what are the chances of finding one?
-You can also find darmanitan as N's Pokemon in desert resort.
-You can get a jellicent in B2 on monday and thursday in W2
-Braviary in route 4 in W2 on monday
-Mandibuzz in route 4 in B2 on thursday
There are many other ways but these are the only wild ones.
-other in game ways are yancy/curtis trades, weather institute deerling but these are not technically wild
No, you cannot. That's why they're Hidden Abilities.
Sources are experience and Game Guide.