There is a site called
"What the book" that is based in Seoul and is similar to Amazon. I haven't ordered from them but I know people who have. If you order over a certain amount shipping is free. I don't know how much shorter the wait time is, as I think that they are simply ordering from the U.S. as well, but the free shipping is nice (as shipping from Amazon can be quite expensive) and you can transfer money to them from your Korean bank account, which is good if you don't have a credit card.
I probably will end up ordering from them if I don't find something in Daejeon soon, I just like going to a bookstore when I need a book to read, not having to go through ordering, transferring money, etc....