Feed stores carry antibiotics for livestock and for blood born infections penicillin is rec. but sounds like Epsom salt compresses maybe needed also. Put some nice warm water into a bowl or bucket add some ES mix well take a clean wash cloth drench in the ES solution wring out just enough it isn't dripping, place over the wound this may help till you've talked to a vet about what you should do. Such a sweet looking duck I hope it makes it through this ordeal.Is there anywhere I can buy antibiotics for ducks?