Most likely Auveco has them. See https://www.auveco.com/. Pretty much every fastener GM has used since maybe 1941 is here: https://www.auveco.com/general-motors. The online catalogs are here: https://onlinecatalog.auveco.com/BookshelfView/
One way to proceed is to match up the part number in the Auveco catalog then find a distributor who has the parts (this is not as difficult as it sounds). A distributor I've used is https://www.dixied.com/. Their site isn't pretty but it is *fast* and accurate and their fulfillment is first rate (I've never had them not fill an order) and their S&H is reasonable. Another that seems OK is https://autofastenersandclips.com/. When you find the clip you want in the Auveco catalog, then cut and paste the UPC for that clip into the search on the autofastenersandclips.com web site and click. (on the DixieID site use the part number, UPC won't work). The part will come up, it'll tell you the pak price and how many are in the pak. For instance, the speednuts that hold the rear shocks come in a pak of 25 for $16.99, UPC is 821641502278. The distributor puts a small-order surcharge on (sometimes this is buried in "shipping and handling" - hint, it's the handling part). Then on either site just follow the instructions to order.