I’m running Windows 10 and my Windows Sounds appear to be in:
C:\Windows\WinSxS\amd64_microsoft-windows-shell-sounds_31bf3856ad364e35_10.0.14393.0_none_4486e7adcc3c3b8e
yours may be different of course.
If you wanted to use the Windows Email notification sound (for example) you could try doing a search for the file name: “Windows Notify Email.wav” and see where it’s located on your computer. Good Luck 