There's two web parts/scripts out there that can be combined to provide
this. The listfolders.vbs from sharepointcode.com will iterate through
and dump your entire folder  structure. There's another web part (I think
from the same site, can't remember) that will display security  settings
for a given folder. Take the code from this and combine it with the
listfolders script and you'll have a dump of all the authors. You might
want to format the output to be a csv file or something then import it
into a spreadsheet or database and remove duplicates.