You could do worse than get one from Paul_S in the UK. He does excellent kits at a very good price (I had one for my 2010 370z). His instructions are excellent and the kit isn't hard to install.
Currently I have a 2016 Z, with the Nissan camera already installed, and I must say that Paul's is better. He's an enthusiast and not in it for the money.
Link -
For Sale - 370Z Reversing Camera Kit (Loom and Camera) - Private Sale - Parts and Stuff - nissansportz