Installing rear fog light on '13 nismo without foglight bumper
 

Title sounds strange, but here is what I'm asking. I have a '13 nismo without the reflector in the diffuser portion of the rear bumper. So in order to convert that would I need to buy an entirely new bumper or could I purchase the carbon signal rear diffuser v1 and install the foglight that way?

I think the cheapest option would be through EVO-R. (Stand by for plenty of hate but I haven't had any issues with them thus far) they make a carbon adapter for the pre-13 models

You can retrofit this finisher to your pre-2014 Nismo bumper and mount the fog light w/bracket to it. Might be cheaper to find a damaged 2014 Nismo bumper with the fog light intact and transfer the parts from that:
B6585-1A30A - Genuine Nissan FINISHER ASMY-R

Alright, so it does seem like there are a couple of options then. Thanks for the suggestions guys.