Try www.trimtags.com, they should have the rivets you need. I don't believe they are installed with a normal rivet gun/tool, they were compressed in place. Others more famailiar with your generation of body style may know more.
Check E Bay out under trim tag rivits # 8065850356 They are listed from 10.00 to 20.00 dollars.Also note in the above listed item the way they are secured ? not sure what's correct .Also read "Trim tags web site for the way they suggest fastening them. Good luck:chev: