Good news / bad news I suppose. Its a shame his previous family can't be found, but since they haven't popped up looking for him there's a chance he wasn't provided with the best home. Now he has a good home, and you've got a new friend.
One thing to look into is his diet. Lots of fresh fruits and veggies is great, seeds tend to be fattening so they should be in moderation. Pelleted foods (Zupreme, Harrison's, etc) should make up the majority of most parrots' diets. However I have heard Ekkie's dietary needs are unique, so some others here can comment on whether pelleted food would be right for him.
Have you brought him into an avian vet? If not it would be good to find one. Not only can he be checked out for any health concerns, but they can give you the best advice on food and care.
If you haven't done so already read through other threads in here. Other than diet air-quality is probably the next most important issue. Household cleaners, air-fresheners, smoke, any kind of vapors such as those from an electric space heater and improperly used non-stick cookware can all pose a deadly threat to birds while we humans wouldn't even notice them.
Its good to hear that some feathers are coming back. That shows you're on the right track. Keep it up and Chives may be back in great shape in no time.