Amprolium for cattle (usually branded as Corid) is what you want. The dose is 2 teaspoons of the liquid to a gallon of water or 1.5 teaspoons of powder form of it to a gallon. I believe you treat for seven days and then reduce the dose by a third for another 10 days. You can direct dose a couple of drops of the liquid into the beak of any really sick birds that are not drinking enough for it to be effective.
PS. Well done for getting a necropsy and thanks for updating us so that we can all learn from your sad experience and perhaps help others in the future.
PS. Well done for getting a necropsy and thanks for updating us so that we can all learn from your sad experience and perhaps help others in the future.