Jayson,
From my understanding, Buick supplied some other "pace cars" for the '83 Indy 500. I've seen pictures, but I can't find any at this moment. The other cars were white convertibles that had the Indy 500 Logo on the side. They were used for the parade and for other activities. Of the two XX models that were made into the real pace car convertibles, one of them was given to the race winner and the other is the one we see at the ROA meets.
I went to
www.Barrett-Jackson.com and scanned their entire list of cars consigned to Las Vegas and no Riviera pace car showed up.
IMHO, I don't see GM getting rid of their one of a kind car unless they got the other back from the race winner.
Ed