duck confit from scratch...
You'll need a great deal more duck fat to confit two ducks than you can get just from them. A few recipes I looked at asked for 6 Cups of rendered duck fat plus the two ducks.
Google is your friend.
Duck Confit 1: http://www.culinarycafe.com/Ethnic_Dishes/Duck_Confit.html
Duck Confit 2: http://www.epicurious.com/recipes/rec...
Agreed. I usually make duck confit after making a roast goose, which renders a huge amount of fat that's wonderful for all sorts of cooking. Some gourmet markets also sell rendered duck or goose fat in plastic vats.
One tip once you do find a good fat source: after you refrigerate the legs in salt & herbs, rinse them off well before you start the cooking process. The first time I did it I just brushed off the excess salt without rinsing them, and they came out way too salty.