Sanborn Maps

A few months ago on one of the forums, there was a discussion on detailed track plans and about where to find them and the industries around them.
I just completed a book on some narrow gauge and short lines here in northeast Georgia. I was quite facinated to watch the industries along the Gainesville Jefferson and Southern and then the Gainesville Midland railroad change from cotton and guano and livery stables to feed and poultry and motor inns.
I also found a track plan for Monroe, GA that appeared to have a Ramsey transfer in the middle. It showed the narrow gauge, dual gauge and standard gauge tracks of three different railroads.
One of the items I found surprising and is logical is the number of overall manufacturers.
I found the Sanborn maps in 2001 at a free download site which has since disappeared. I thought it had been the Library of Congress collection but they have told me the project digitizing the 660,000 maps of 12,000 cities has been suspended.
Doug