Original Gift deed is missing

Sir My deceased father acquired a lease hold 3 katha plot (999 years) from West Bengal Housing Board in 1986 through a Lease Deed. He was paying Kolkata Municipal Corporation Tax there on. In the year 1993 my father , due to fragile health , got the lease hold right of the plot transferred in my name vide a permission from West Bengal Housing Board in April 1993. Incidentally I am the only child of my parents. On the basis of such permission , My father , made a gift deed in my favour in August 1993 in the Registrar office Kolkata. Consequently , a certified copy of gift deed was issued to us and on the basis of such certified copy , the land was mutated in my name and since then I am paying the Municipal Tax of the land . We have not taken the Original Gift deed from the Registrar office since 1993. I have the Original Lease Deed with me and the certified copy of Gift Deed. But I do not have the Original Gift Deed. I have approached the Registrar office with the original IGR for delivery . The clerks of the Registrar office said such a old Gift deed of 25 years is not traceable . Now I want to sale the property but buyers are asking for Original Gift Deed. PLEASE ADVISE what to do in order to satisfy the requirements of the buyer ? From : Partha Pratim Chakraborti , Kolkata -700061