Your measurements shoudl line up with one or more of the GM push retainers on this page
https://www.auveco.com/push-type-retainers
then with the auveco number you may be able to order from Dixieland, Zoro, or other source. Put the Auveco number into the Dixieland search box, it should be there to purchase: https://www.dixied.com/cgi-dixied/sb/productsearch.cgi?search_field=17162
HOWEVER, watch out for the $45.00 minimum. You may need to find a retailer.
Alternatively, do a web search using that part number. Might be Auveco 17162 or 19297 or other -- you'll need to look at the description and match up the head diameter, and depth, and what size hole it's supposed to go into. The descriptions will tell you what panel range (how deep a hole) is OK for the fastener and so on.
Also, don't be surprised if these are available from the GM dealer even though they are 'discontinued' for the Riviera.
