Check the link http://www.aav.org/association/index.php?content=activeMembersList
for avian-experienced members of AAV in your area or call your regular vet and see who they recommend. They do not have to be board-certified, but must have plenty of practical experience.
Feather damaging behavior can be caused by a multitude of things, including bacterial skin infection,viruses, fungal infections, allergies, metal poisoning, hormonal flux, psychological or combinations of these factors. The difficulty is diagnosing the problems and assigning an intelligent treatment plan. Your vet will want to run a number of tests so that appropriate medications can be prescribed. A behavior consultation may be recommended to to assist training both bird and people to better behaviors.
This is a common area to be damaged if the bird has an inflammatory skin/follicle disease. The causes can include local infection, metabolic problems, or even intestinal parasites. It can also be a prime area for even more serious problems like skin cancer. An avian-experienced vet should take a look at him, and run some tests. If he were my patient, I would start with complete fecal analysis and direct smear, bacterial culture and sensitivity of the feces, skin, feather pulp, and choana. Depending on the case I might do a fungal culture. Routine blood work is necessary to rule out other issues. Generally I start them out on antibiotics as indicated by the tests (I use a lot of human antibiotics that are injectable) and an anti-inflammatory such as ibuprofen.
Pet/feed store medications and home remedies are harmful, ineffective, immuno-suppressive, and make them much worse and may interfere with the veterinarian's diagnosis and treatment. Do not use them.
Here are some other suggestions:
Birds should be on a high-quality, preferably prescription, pelleted diet. In addition, they should be offered dark leafy greens, cooked sweet potatoes, yams, squash, pumpkin; entire (tops and bottoms) fresh carrots and so forth. No seeds (and that means a mix, or millet, or sprays, etc etc.) and only healthy, low-fat high fiber people food. A dietary change should be closely monitored and supervised by your avian vet.
Birds should get 12-14 hours dark, quiet, uninterrupted sleep at night. Any less and they can suffer from sleep deprivation and associated illnesses. They should be covered or their cage placed in a dark room that is not used after they go to bed. They should have access to bathing by daily shower, misting, bath bowl, etc.
The cage material should be cleaned everyday, and twice a day if the bird is really messy. Paper towels, newspaper, bath towels are ok. Never use corn cob, sawdust, wood chips, or walnut shell. Consider getting a large cage that is longer than tall--as birds move in a horizontal rather than vertical orientation; and have several feeding stations.
Never give grit, gravel sandpaper or cement perches. A bird will eat those to excess when it is not feeling well or if there is a nutritional deficiency. They do not need it at all (an old myth from the poultry days, even poultry do not need it). It can cause an impaction and lead to serious or fatal consequences.