Does anyone know where I could purchase volume 6 of this manhwa?

Me and my friend bought vol. 6 at on line manga shop from Manila, it's called Eiwa Mangastore. The price for this volume wasn't high. It was 2 months ago and Eiwa don't have this vol. in stock anymore. For now, the prices of it are incredibly high - about 200$, or even more (on Amazon). Anyway, I wish you good luck, maybe you'll find it in normal price et ebay! BTW - I'm totally captivated by this unique story <3