Idunno about where you is but in CA you can have the seller fill out a "Statement of Fact" form from the DMV saying he lost the Title. That and the Bill of Sale would let you get a new Title.
A shady way to do it if you're sure it was his with a clean Title and he just lost it would be to go to the DMV and do the paperwork for a lost Title in your name.
Sic friatur crustulum
'84 GW with Nissan SD33T, early Chev NV4500, 300, narrowed Ford reverse 44, narrowed Ford 60, SOA/reversed shackle in fornt, lowered mount/flipped shackle in rear.