Originally Posted by Zacharias

The dealer can supply them for something like $3 each, last time I was unlucky enough to have to buy some there.

There is a guy on eBay, in Thailand if I recall correctly, who sells them in large packages. I purchased some last year. I don't remember his user ID right now.

I tried looking and found this guy, in the US, but he sells in packages of 10:
Mercedes r107 w123 w126 r129 door Moulding CLIP ( x10) grommet fastener inserts | eBay