Check your craig list ads sometime feed stores will also have postings. And here on BYC we have a rehoming thread and a buy sell trade thread just keep scrolling down past the duck forum.
Could have been a pred then and maybe something scared it off before it had a chance to out right kill...
I'd try and find your duck a friend ducks are flock animals and really like to have one of their own.
I am very sorry you lost him :hugs
Is their pen and coop secure so nothing can get in. Minks, weasel are small enough to get through 1" wire this could have been an attack by a predator. Look...
If your Guinea gets along with your chickens keep her but remove your ducks from having to be in same coop and pen. Not all poultry get along.
Are you sure these are the only 2 wounds on your drake? can you post a pic of the wounds