The name space and intellisense information, for the CLR, comes from a database hidden inside the VS install.
The information for the working project, is scanned and archived (I think in a file) when you open the project. It then periodically updates it as you work.
If you want the exact path, I doubt that Microsoft publishes that information.
After looking at your other question, I wanted to add that it is possible (somehow) to have Visual Studio rebuild the index information for a given project. It eludes me on how to do this right now. Have you tried this and did you end up with the same results?
Update in regards to comments:
Refreshing the cache is easy but not
necessarily obvious. There are two
ways to refresh the cache: 1) Go to
Edit -> IntelliSense -> Refresh Local
Cache and 2) Hit Ctrl+Shift+R
Source: Dan's Blog - Refreshing the IntelliSense Cache