Have you tried the obvious? Check with Fastlane or Mercedesshop and see what their price is for the exact oem replacement.
I'm not looking to get flamed by the audiophiles out there, but the front dash speakers on my '91 300TE 4m were < $30 apiece when I priced them. I think this was from either Fastlane or benzbin. You know they will fit and I'm not sure why anybody needs a 5 MW system in a car. The premium sound package that came on the 4matics has always been plenty for me. I even turn the bass down from the normal setting because it gives me a headache at the normal settings.