You can download the VRPN source code from here:
Simply open the vrpn.sln solution file in Visual C++ (works in Express as well) and do a Release build. You'll get a DLL in pc_win32\DLL\Release.
Also, I think it's possible to link native code statically into an executable that uses the CLR, but I'm not sure of the details. That would eliminate the need for the DLL entirely.
Also, this site claims to have a C# wrapper for VRPN:
I haven't looked into that.
Hope this is useful!