If you are looking for homes that have already gone through the foreclosure process and were unsuccessfully sold, you can check the web sites of most major national mortgage companies. These are called REOs (stands for Real Estate Owned).
You can also try and catch the property before it is foreclosed by the bank at auction. These auctions take place on Thurs. @ 3:00 p.m. in Room 274 at 360 Adams St.
However you can really find some great opportunities and prevent the home from the extra expense (forecloses can cost the bank an average of about $60k), plus save the homeowner from having a "foreclosure" on their record, by reaching those homeowners before it gets forecloses. Sometimes real estate agents, like myself, subscribe to services that provides them with properties that has "lis pendens". This is what mortgage company files to let anyone who is looking at the property records that their is a pending law suit.
To give you an idea, I just found 110 properties with lis pendens files within the last 7 days in Brooklyn.