I wanted to include some DLLs in a package, I found a trick to allow you to get those DLLs from the GAC from Geeks With Blogs

In RegEdit, navigate to:
HKEY_LOCAL_MACHINE\Software\Microsoft\Fusion

Add a DWORD (32-bit) value ‘DisableCacheViewer’: decimal value – 1

Then navigate to the GAC at c:\Windows\Assembly to find the DLL.