I have a 2012 335i E92 with the M package. At my request, my CA put a set of the BMW black performance grills in the trunk for me when I took delivery. I installed them when I returned home and if I recall, it took about 30 minutes. I followed the DIY on this site - very easy.
Here are the part numbers off the boxes:
R - 51 71 2 158 984
L - 51 71 2 158 985
You should verify these in case there have been any changes since May when I took delivery!
2012 335i X Drive Coupe - BSM/Black, 6MT, M Sport, Premium, Navigation, Apps, Black Grille, 313 Wheels, and more...