Just type in google 미남당-사건수첩 책

You can buy it on yes24, here:

http://www.yes24.com/Product/Goods/59618175

Aladin.co.kr  has ebook format available:

https://www.aladin.co.kr/shop/wproduct.aspx?ItemId=147989762

Thank you so much @figyelka 

Just another question, would they have translations or is it in Korean only?

It's only in Korean. There is no English translation for this book. :(

Oh no ?

Thank you so much for your help tho!!!

I wish it was an English version.  I would think this book would be a good read 

Especially compared to how weirdly the show is going rn with pacing and all. Cause the premise sounds freaking superb but the acting and writing leaves much to be desired

Not sure it will really help you, but the original novel has been translated into French in 2020, you can find the ebook at https://play.google.com/store/books/details?id=3jH4DwAAQBAJ

I thought I would leave the info here for fellow French speakers ;)

Hopefully they will also release an English translation soon, fingers crossed!

Thank you so much for sharing the link, I speak a little French maybe this can be an incentive to practice for me