Question

Where do you find the power herb?

Answer 1

You buy it in the Battle Frontier for 32 BP.

Comments

In diamond that would be battle tower.

Answer 2

You can also get it (if you have SS or HG) below GoldenRod
City if you go left from the breeders house in to the water
and down.

You will have to battle 3 trainers first.

You get it as a prize.