I have been looking for those ever since I bought my car. NYS is a two plate state. I must confess that I cheated and used some torx screws that I got from the "Help" display at the parts store as I couldn't locate a GM P/N to try to order them from a dealer. I gave up mostly, as the stuff I bought was like the wheel house panel screws only a smaller thread size. Absolutely no good for the NCRS crowd.
The standard stuff that places like MAM or CC sells are not for our license plate screw bosses, even though they are listed as license plate screws.