The one inside the wheel well is for the sunroof. If you remove the plastic linner you should have acess to it. But I have only been in their once and I don't really remember. Hopfully it doesn't run all the way up to the pillar!
As far as where to get it, I'm sure the dealer's parts diagram will have it listed. Maybe if you look at the break down on the screen that will give you an idea of whats involved in changing it.