cars selling dealership ?

ok, I've been trying to research my cars history. I've gone back to '88. How the hell can I find what dealership ordered and sold my car back in '70 ? I have the broadcast sheet and vehicle order number but can figure out where the car went after the build. I've got a detective buddy and a cousin that works for the state department in DC looking into if for me, but no luck yet. Has anyone been successful in tracking this info down ??