There are a very few organizations that rescue and adopt out ducks, but there are also informal networks of people who rescue abandoned ducks here and there.
Here is one I know nothing about, but did find a link to.
http://farmanimal.rescueme.org/Connecticut
There is also Majestic Waterfowl in Connecticut,
http://www.majesticwaterfowl.org
Then there is
http://www.petfinder.com/shelters/MA147.html
which I have heard of, but not worked with.
In Tennessee, there is Feathered Angels Waterfowl Sanctuary.
And I heard of Carolina Waterfowl through BYC DF
http://www.carolinawaterfowlrescue.com
Web searches using keywords like waterfowl, "farm animals," rescue, adopt, can turn up some of these. There is also a horse and livestock association in my town, and they are good with helping locate critters. Even Craigslist can be a source.