Lost my receipt of payment made to builder

Dear sir/ madam My name is Ravi, and i need an advice from experts regarding my sale of apartment in Dombivli. here is the case in details. 1) My mother own a property her name in dombivli, we are the first owner of the flat brought in 1990 through bank loan. we posses all the necessary documents like sales deed, maintenance receipts, tax receipts, noc from society, title of the property is clear, the property is conveyanced in the name of society and other documents in the name of my mother. apart from just one document that is full payment receipts made to builder, now either it is lost or not provided to us. 2) I have recently decided to sell my property in dombivali (kalyan dist) to a prospective buyer who wishes to buy my flat through Bank loan. we have registered the sale agreement and submitted the same to the buyers bank for loan procedure. 3) Now the bank is demanding payment receipts made to builder for processing the loan, which obviously we do not have. To make matter worse the builder is now deceased and his company has closed in 2001. thus we cannot contact the builder for the same. Now the loan procedure is stuck for this single document which we obviously cannot furbish. 4) Now i would like to advised is to how should we proceed further what supplementary documents can we produce to the bank on its behalf or is there any way to get duplicate receipt in the absence of the builder. and 5) Is there any way that the bank can sanction loan to my buyer without this piece of document at present. What should be my further course of action kindly suggest as i am in need to sell the above property. Thanking You in Advance