This should be no problem of course, as the first two assemblies show up in the .Net reference list:
The answer is the platform agnostic GAC (%SystemRoot%\assembly\GAC_MSIL). Its contents are seemingly invisible to searching: the only way to access them is:
- Via the command-shell, e.g. via a command-prompt, cd/explorer into %SystemRoot%\assembly\GAC_MSIL.
- Via Microsoft's gacutil.exe.
Doing this allows you to locate the third assembly at: