I might be a bit too late for your Korea trip with my reply, but for anyone else planning to visit the country: there is a MASSIVE electronics shopping mall in Yongsan, Seoul. It comprises 20 buildings with over 5,000 stores and my local contacts tell me that if it's electronic and exists, it can be found there, and cheaper than anywhere else.
But if you don't know where you're going inside the complex, you're in for a rather hard time, as you might imagine considering the size of the place. I've also heard that haggling is an important part of shopping there, and that the merchants are rather aggressive in offering their goods to you, so you better be prepared for that.
