if the file is not available how would you transfer the car? if you are dead determined to buy because of papers getting cheap, pay an agreed advance and ask owner to register an FIR for file and submit an application for duplicate papers, use some agent to get it sorted. Get transfer letter signed by owner without date & hold 10% payment only till such time papers are ready and ready for transfer in your name. by all means papers will be reissued with an stamp " duplicate ", transfer the car in your name, with all papers / duplicate file intact car value will enhance approx 10 - 20,000 because papers are available but with duplicate stamp.
else, as it is without papers - RISK is high., your money your call to play wager.