I assume you mean Iron First.
To get Hidden Abilities you can get them via the Pokemon Global Link either through the Pokemon Dream World or a Global Link promotion.
Some event Pokemon have their hidden ability and Pokemon from the Dream Radar will also.
Also in Black/White2 in the Hidden Grottos the Pokemon you capture will all have their Hidden Ability but I'm not sure if Ledian is one of the Pokemon catchable from the Hidden Grotto
~GL getting Ledian's Hidden Ability!