I saw these wheel covers at this site http://www.autoguide.net/apf/mercedes-wheels_rims/index.html
they also have the steel wheels another place to try is Canada I purchased my 16" wheel covers for my W124 wagon from Vancouver Mercedes
1395 Broadway West
Vancouver, BC V6H 1G9, Canada
(604) 629-2210 Speak to Geoff in parts he can get many Euro parts that the US deals tell you they cannot get
mercedes-benz.ca