I EV train, and I care about natures.
I must suck.
There's an EV training help thread in the BW Discussion forum, but watevs.
If you get 5 SpA per battle, you'll only have 250 SpA at the end of 50 battles. After doing that, you would need to battle two more Litwicks/Elgyems without using the Power Lens (or one more using the Macho Brace).
Bear in mind that Pokerus doubles your overall EVs, and steroids at 10 EVs to their corresponding stat. If you give your Pokemon 10 Calciums, you'll only need 152. With Pokerus, you only need to battle 15 Litwicks/Elgyems with the Power Lens, and then one more with the Macho Brace.
The same applies to Speed, but since Basculins give two Speed EVs apiece, you would earn 12 EVs total with the Power Anklet. As such, after giving 10 Carbos, you would battle 12 Basculin with Pokerus and Power Anklet, and then two more Basculin with Macho Brace.