Yes you need to look for the "Gold version" of the game.. as it's enclosed with it.
There's also a Special Limited Edition, but this one does not have the soundtrack.
Both versions have 4 discs for the game itself, and the "Gold ver." have a 5th disc for the soundtrack.
I think you'll have to order directly from a Korean shop.. or find it on ebay (probably very small chance).
Make sure you see the little yellow sticker on the box with "gold ver." on it.
Shop i found (all in Korean - good luck):
naver.com
Another thing you can "try", is to email Mr. Kwang, it's a reliable Korean shop (they sell a few Korean soundtracks - but don't have this one -)..
and they'r taking requests (check main page) by email.
Mr. Kwang website