A brief glimpse of the 1968 Camaro RS/SS convertible used by Martinsville Speedway during their 1968 NASCAR sanctioned events can be seen in color footage taken during the 2nd annual Dogwood 300. This was a NASCAR National Modified Championship race. It was the first event held at the track for the 1968 season and it was won by Carl Bugs Stevens. I'm not sure if the Camaro was used to pace the race or if it carried dignitaries around the track on the parade lap like it did at a few other races at the track.
I found the footage in the WSLS-TV (Roanoke, VA) News Film Collection. See the Camaro at 1:29 here: https://search.lib.virginia.edu/catalog/uva-lib:2216898
I couldn't find any other pictures of the event or the souvenir program. I did find an article previewing the event at www.edflemke.com