Hi,
I bought a really old map from the Wandsworth historical society a couple of years ago. But it is newly printed, a reproduction of a 1787 map from British library. Very interesting to see the land pre the mass building.
http://www.wandsworthhistory.org.uk/publications.htm
Otherwise the Northcote Antiques market sometimes has some local ones. And eBay has quite a lot.
Good luck with your search