Where do you find the dragon scale in black/white?

Question

I want to know so that I can evolve my seadra into kingdra.

Answer 1

You can find one on Route 13 and Route 18 and on wild horesea, seadra, kingdra, dratini, dragonair, and dragonite for 5 %.

Answer 2

There is also a man dressed in black near a house, along the shoreline of Route 13 which gives random treasures to you daily (including a Dragon Scale!).

To get there, fly to Undella Town, and make your way up. After the pass, go up, and towards the left past the trainers. Afterwards, start going north (not all the way), and find a house, and the man dressed in black will be outside of it.