Finding decent board games is really tough in Korea.

I recommend using koreaboardgames.com

They have a decent selection of games and many of them are in English. The site mentions the language that the game is in so you shouldn't get stuck with an international game translated into korean unless you really don't pay attention or if you wanted it to be in korean.

Other than that site, I have found the odd good game (Carcassonne, Stone Age, Settlers of Catan) at various chain bookstores in Busan and in Seoul. My method is to keep an eye open every time I go to a large(ish) book store. You just never know... it is possible to get lucky. However, it is like finding a needle in a haystack!