I was in the same boat, tried the Classic Centre in Stuttgart and got this reply
We apologize, but we (Mercedes-Benz Classic Customer Center) are not able to issue a data card for your vehicle.
Please contact your local Mercedes-Benz dealership in your home country to apply for a data card.
The department for service and parts is able to provide a data card for your vehicle.
Thank you for your understanding.
Kind regards
Mercedes-Benz Classic Contakt Center / MHO
Tried the local MB dealer who referred me back to Stuttgart...
Anyway, after a bit of searching, I emailed these guys and got a copy of the data card by return:-
ClassicParts@sandown-mercedes.co.uk