You are aware 19" wheels were not standard fitment? LMGT4's (not black) were available as a £2.5k option IIRC, but not sure if they were the 18" or 19" options Some early imports were on 17" wheels.
Yes, there are quite a few gunmetal/alezan 350's around, but the alezan was a £400 option (UK models) and there are many with the charcoal black leather about and few non-leather ones as well.
I presume it is a coupe you are after, and just to note that if it is a roadster you wanted it does not have bluetooth capability (in case the phone integration you are thinking of does not have its own )