It would be best if you posted some code to show us how you're currently getting the first video device. Although there is
a project to get DirectShow working in .Net. Look at question 8 ("can I work with multiple video devices at the same time?") on
this page, which shows how you would work with extra video devices, at least using that library (if that's what you're looking for, you could download their code and see how they implement that call to DirectShow).