My local feed store carries ducklings but they are not sexed. It cost more to buy from a hatchery and is a bit stressful while they ship but was worth it for me. I only have a backyard flock so no need for mating or babies. ;)
Darker heads than the body, darker feathers on the back, greenish bills, more orange on the legs, feather tail curl and raspy instead of loud quack indicates male. Is this what you are seeing and hearing?