Kings rock or water stone in pokemon black/white?

so i was training one day on my pokemon and i felt like fishing. the first thing that i snagged was a shiny poliwag! its now a shiny poliwhirl but you cant really tell its shiny. so i want to evolve it. i already used the water stone i got from driftveil and i cant find a kings rock anywhere. so if someone out there would want to trade me a pokemon with a kings rock or water stone that would be great. preferably a water stone. thankss