You'd have to collect it at one of these places.
http://www.egsimcard.co.kr/eng/buy-e...to-collect.asp
I've never used this service, so don't know any other details, sorry.
I always recommend visitors get a KT Olleh Wifi Egg while they're here. It's 8,000W per day with a 200,000W refundable security deposit. 4G data, works everywhere, and you can share with everyone in your group. If you show your Korean Air boarding pass, you get a discount. My father just did.
Unfortunately, the KT Olleh pick up counter closes at 10 PM.