Motorbike (Oldie) without registration (ZB 1)?

3 years ago I bought an old Honda (year 1988) (in parts) and rebuilt it, I only got the ZB 2/Vehicle letter when I bought it, the previous owner had no more, he had had had them standing around forever, and never registered on himself. The letter has a registration from 2004, was apparently applied for again. The owner, who had the 20 years ago, can no longer be identified. At the registration office they want the ticket (ZB1), or an affidavit. clarification of the person to whom the machine was last registered, that the bill has been lost??? Am despairing, does one have an idea? Nice evening off