It's just Special Attack EVs in Black. The only things that give out Special Attack EVs early on in Black are a couple of in-game trainers' Petilil. I don't get an ample source of Special Attack EVs until I get to the Celestial Tower, which is mid-game (Litwick and Elgyem give out Special Attack EVs). In White, I can EV train against Petilil for Special Attack in Pinwheel Forest, despite Oshawott/Dewott's Grass weakness.