The stainless steel overlays used to be on eBay all the time. I don't recall seeing them for long time now.

The cover that looks like this but is plug-n-play would come from an SLK.

The covers in the pics look like the 2 piece version. You will need the airbox, and front engine cover(for a v6). The same airbox is used on the v6 and v8 with different engine covers on the front.

I think this is the airbox you will need: http://www.ebay.com/itm/2003-Mercedes-Benz-C240-Airbox-Cleaner-Assembly-112-090-15-01-OEM-/161677168204?hash=item25a4b5ce4c&vxp=mtr
Here is the v6 engine cover that took me a while to find for my car: http://www.ebay.com/itm/01-04-Mercedes-C320-engine-cover-nose-piece-1120100467-NL0028-/261693738639?hash=item3cee298e8f&vxp=mtr
Others will chime in for a perfect fit with the correct part number.

James