Apparently this keyboard store (pretty well known here at Geekhack, actually) has an actual store in Seoul:
http://leopold.co.kr/I'm not sure how you'll travel, or if you know Korean at all, but perhaps you could present this address to the person (I'm assuming taxi driver) who'll transport you: 서울특별시 용산구 한강로 314 용성비즈텔 1607호 레오폴드(주)
I can speak and read Korean decently (but not fluently), and from what I gather of the address, and what I remember about Korea, this keyboard store will most likely be in an area called "용산", which is basically an electronics district, almost like Akihabara of Japan (but not quite as big). The district is pretty centrally located; it's definitely IN Seoul, and pretty close to its downtown, IIRC. And in that district, the store will be in probably one of the many malls there, specifically "용성비즈텔", and will be located within that mall in location 1607.
Hope that helps. That was the address listed on the Leopold site. Pretty sure that's the address to their actual store front, as I just saw that address mentioned in a thread regarding warranty repairs on their message board.