How do I find files that are missing from visual studio projects?

Question

Due to issues with merging etc, we have lots of project files that don’t contain all source code files that are within their folders.

Before I write a little tool, that

Answer 1

(Assuming that Team Foundation Server is your source control): If the file has been added to the project and shows up in Source Control Explorer, but does NOT show up in Solution Explorer, you must manually add it to Source Control Explorer by selecting "Add", "Existing Item". This is an annoying Visual Studio/TFS bug that I just spend 2 hours trying to figure out.