I can help!! I answered by editing your original post. They don't tend to be the greatest layers though. About every other day for half the year. All depends on the strain.
www.johnsonswaterfowl.comhas Holderread stock runners from what I have heard. I've ordered twice from there. They can be unreliable at times, but I have gotten my ducklings both back ones. I would go for at least 4. Johnsons minimum is 6
@Ravynscroft has some that I believe are nice birds and if your fine with adult birds www.duckcreekfarm.com is Dave Holderreads nephew and has al of his leftover flock. You could also try on the call duck thread.
Does it have a really loud and sharp QUACK or does it have a raspy low quack? The females will be the first one I described with the males being the latter.
Mallard boys will have green bills at that age and the girls will have brownish orange bill, however you do need to listen to their voices for 100% accuracy.