If it is not for a newish car , you can write to the Classic Centre in Fellbach , enclosing proof of ownership ( copy of registration document ) as required by German law .
They can provide this information from the archives , when I did this in the early 80's for my Ponton , I received back a very nice letter from Herr Von Pein and numerous documents including the requested information , data card , windscreen consignment sticker , factory photographs and more .
Nowadays , you can request a vehicle 'birth certificate' which is accepted by DVLA as proof of date of manufacture for registration purposes , although there is now a fee .