Update!!
I went to the Cultizm shop, which has moved to near Sinsa station. The staff are amazing, and the place was full of denim nerds. They have an almost complete line of Nudies, all of which are actually cheaper than they were back in Canada. I got a pair of dirt dry organic Grim Tims for 190,000.
Highly recommend it. They don't speak much English, but they know their stock ridiculously well. If you have any questions, someone will be able to answer you, even if there's a bit of a language barrier.
Now - time to break these Tims in before summer comes!