Here’s an NOS Sport mirror for the 70-72 GS that has been sitting on eBay forever. Likely because it is a bit high on price. I think the guy said the date code is 10-DMI-0. Might be able to message the guy to see if he’ll drop the price. https://www.ebay.com/itm/4010394181...AbKvL7pQMu&var=&widget_ver=artemis&media=COPY
Here’s another one of later year but NOS and has the correct assembly part number. Appears to be 73-76 GM replacement part but should work for our 70-72 Buick Skylark/GS. https://www.ebay.com/itm/2250474365...AbKvL7pQMu&var=&widget_ver=artemis&media=COPY