I got one just by asking.
I sent an email to the Chevrolet Store web site asking if they offered the posters for sale. My email was passed on to the ad agency that did the photo shoot.
I received a reply from them stating that they were not making these for public sale, but that they did make some as gifts for some Corvette engineers. I was then asked if I wanted one because they had one left over, sitting in the corner!
My answer was of course YES and two days later I received the 24"x36" poster pictured above. No charge, not even shipping.
What a great company!