I have two Blue & Gold Macaws and one has been losing/plucking his/her feathers for 6 months,?

Finding him a new home may just make him pick more. Take him to the vet, he may have a medical problem or burrowing mites. A pelleted diet is much better than seed, it has all the nutrition they need without having to give them supplements. Remember, when you buy a large bird, it is a commitment to them. To them, you are part of their flock. Birds suffer mentally when they go from owner to owner and can develop many bad habits, some of which are harmful to them. Bird rescues are full of birds where the owner just decided to give them a new home. Many of them can't be adopted by people because they have now developed such bad behavior.