I couldn't find it via Googling, but often times you can find where it's stored via checking what the game's AppID is. AppID is usually shown in an ini file where the exe is in the game directory. It's a string of about 6 numbers and if you do a file search for it in Windows, you might find it's location. There is often a folder with that number as it's name contained in the same place the saves are.
That said, don't be surprised if you can't even find it. Someone on the Steam forum asked on The Haven Moon forum where the saves were, and all the game dev told him is saves are automatic, and you don't need to access them to see a different ending.