Hi,
if you have the acceleration dvd, search for the file scenery8.cab.
Open the cabinet file with winzip etc and look for
scenery.global.scenery_autogen.bgl
copy it to the appropriate FSX directory and rename it to autogen.bgl.
With standard FSX DVD / old versions I'm not quite sure, I think that finding the file there could be difficult, because the name in the cab file is not so obvious as above.
Cheers,
Mark