It sounds like you are trying to do something with a add-in that was created in Visual Studio (or some of the MS Express development tools). VB or C# (likely C++ as well) compiles the created plug-in to a dll called "project_name".dll. swvbaddin is the default name for the first add-in project if I do not remeber it wrong.
I would say that it is impossible for anyone to say where you can find the correct dll file that you are looking for. You have to get in touch with the one that developed the add-in.