There was another thread on this issue a month or so ago. This is the response one of the members provided:

" I don't have the part number in front of me but you can get them at a Mercedes dealer, it's a standard Mercedes item. I had to order them but they were inexpensive and only took a few days to get. "

So, you may want to check out a Mercedes dealer. The other option is buy some new mats that come with the clips. You'll have a spare set of mats and the clips are interchange able so once you wear these out, just switch out the clips with the new ones. You can find the original mats for pretty cheap..........between 30 and 60 bucks last I looked.