it didnt come with it? Ied assume you could buy the stock camera and check the TIS for a wiring diagram and just intergrate it.
I doubt it would be "hard" as no camera is truely hard to install, its just time consuming because you have to mount it and run the wire all the way up and splice in somehow.
There is a thread on this recently (regarding the compatibilty of different generations of nav). I asked the same question. IIRC, you need a gen-4 nav or the second ecu that handles the camera operation. There are two plugs in the gen-4 nav, one is the same as the gen-3, the other controls the camera and some other stuff not found on the gen-3.