I bought it on booksonkorea last year, but you’re right - I checked my link and the page for it is gone, it just pops up with a ‘book not for sale’ notification… Annoying, because you can still buy the rest of the books in the series individually… 
It might be worth looking into a proxy service for a quote - I haven’t used any from Korea, but @eefara recently got a Korean copy of a book using one:
