You can find the entire 7-book series on Amazon Kindle . The books are also available as audiobooks via Audible and Storytel .
If you prefer DRM-free copies, GOG is your best bet. You download an offline installer, meaning you own the game forever without needing an internet connection to launch it. Download Shades Of Sin English Version
For those interested in exploring the concept of sin further, additional resources are available: You can find the entire 7-book series on Amazon Kindle