Very happy news, Baymule!
Find niacin capsules, not no-flush, not timed-release, not tablets. Storey's Guide to Raising Ducks recommends for ducklings showing signs of deficiency, to use 100 to 150 mg niacin per gallon of drinking water for several weeks.
We don't have a hard and fast concentration for preventative measures, but I would want at least 50 mg per gallon, and would likely myself go with 100 mg per gallon for the first 8 weeks.
Some folks sprinkle brewer's yeast on the food. That is less precise, but they report that the ducklings do well with that approach. According to this web site,
http://nutritiondata.self.com/facts/custom/1323569/2 brewer's yeast has a number of other nutrients in it as well, and ducklings can also have thiamine deficiencies. That is another B vitamin. I have heard some use B Complex, not just the straight niacin.
We all do the best we can with what we have, and I think that gives rise to many different ways of caring for our animals.