If Tokyo, go to Korean Town in Okubo just beside Shinjuku. Lots of Korean BBQ there.
Another is in Ginza called the Carne Station. Its a yakiniku but its more Korean than Japanese. The Kimchi there is really good. Its just 1000yen for 1 hour, eat all you can
In Osaka, I have not found any Korean yakiniku though I found a really nice Korean restaurant already.