There are aftermarket options so far i found the following. If I do purchase plan is to run the wires to the trunk and splice into the brake power wire on the Diode Dynamics tails harness. There really pricey though.I believe they are different 17+ had a refresh in design so you would need to find a 17+ rear diffuser been looking for one haven’t had any luck
option 1

Phoenix's Power Carbon Rear Diffuser Panel + Fin Set (Phoenix's Power x Garage Fukui) for 2011-19 Nissan GT-R [R35] - Bulletproof Automotive
Phoenix Power x Garage Fukui's aero kit for the Nissan GTR R35. Distributed worldwide by Bulletproof Automotive
bulletproofautomotive.com
option 2

2012-2020 Nissan GTR R35 DBA/EBA NSM Style Carbon Fiber Rear Diffuser w/ LED Light
Darwinpro 2012-2020 Nissan GTR R35 DBA/EBA NSM Style Carbon Fiber Rear Diffuser w/ LED Light Condition: Brand New Material Option: CFRP/FGCF/DryCF Fits 2012-2020 Nissan GTR R35 DBA/EBA Package Contents: One carbon fiber rear diffuser w/ LED light Part No: CF3505NSMO.RD CF3505BKSS.RDCRD Have...

option 3

Top Secret M17 Rear Under Bumper for 2017-19 Nissan GT-R [R35] - Bulletproof Automotive
Rear under-bumper for MY2017 GTR onwards.
bulletproofautomotive.com