I've noted several posts over the months saying that the local Mercedes dealer will provide a "VMI" if asked.
So far, I've tried two different dealers in the Washington, DC area and got two different responses:
First- Sorry, your 1996 is too old. VMI's are only for newer cars. (he DID give me my radio code though)
Second - Did you buy your Mercedes here? No? I'm sorry I can't help you...

You guys must have more cooperative dealers than I have around here...

KenP