You shouldn't have any trouble finding the maps you need.  Many maps from
the Revolutionary War era (including the Sauthier 1779 map of new York) are
available from the American Memory site at the Library of Congress.
http://lcweb2.loc.gov/ammem/gmdhtml/gmdhome.html.  You should also check
the David Rumsey site at www.davidrumsey.com.  Among other things you can
find there Christopher Colles' Survey of the Roads (1790), which is more
detailed and accurate than the British maps of the colonial era.

David Allen
Map Librarian
SUNY Stony Brook