Although I feed all organic from both my local feed store and co-op, I've seen chicken feed available at
Wal-Mart. Some stores you can check into to see if you have one around besides your local
Wal-Mart:
1. Cal-Ranch
2.
Tractor Supply
3. Any local pet stores...
You don't have to find feed that is specifically made for ducks - most people just feed unmedicated chick starter, then switch to a grower/flock raiser for the rest of their lives. Just provide oyster shell on the side once they start laying their first eggs. The other thing you will need to provide (if you have ducklings) is regular niacin (NO "flush-free", "no-flush", or "time-release"). They should have 100-125mg added to their water for the first 10-12 weeks. It's important to their overall health and leg strength.
As for house foods, they pretty much love anything green! Romaine, arugula, kale, mustard greens, dandelions/greens, etc. Limit the spinach, however. They will attack you for frozen, thawed peas! Peas also have niacin, so that's a great treat! Some people throw out most of the same type of scraps that they throw out for chickens, but my ducks have never been interested in much of anything that wasn't green & leafy. They do love watermelon though!