Since I barely ever use Windows myself I can't really help any more than point to the Unity documentation for where you can find the PlayerPrefs file. I'm not familiar with the Windows registry at all, so I don't know why it wouldn't be there. Did you follow the exact path given by the documentation?
"On Windows, PlayerPrefs are stored in the registry under HKCU\Software\[company name]\[product name] key, where company and product names are the names set up in Project Settings."
I will definitely fix this issue once I get time to work on this project again (probably the end of next month)