I'm sorry that your question wasn't answered in a timely manner. We don't have many avian-oriented vet on this site. Head shaking still presents an enigma. While mites are usually the first thought, many times no parasites can be found, the ears aren't infected, no evidence of upper respiratory infection - swollen sinuses, nasal discharge, oral lesions - is seen and we're left thinking it represents a behavioral quirk in some birds. When mites are a problem, more than one bird is expected to be symptomatic. Please first check his ears - you may have to "hog-tie" him but we don't want to overlook something simple such as foreign material lodged in an ear orifice. Take a look into his oral cavity and see if any lesions are apparent. If nothing untoward can be found, here's how mites are addressed:
One study compared mite populations between hens that were caged, free range, and free range with access to dust boxes containing sand and either diatomaceous earth, kaolin clay, or sulfur. All hens using dust boxes with any material showed a reduction in ectoparasites by 80-100% after one week. Ectoparasite populations recovered when dust boxes containing diatomaceous earth or kaolin clay were removed; however, sulfur provided a residual effect up to nine months post removal. As you can see, provision of duct boxes is a simple and effective method of ectoparasite control for backyard flocks.
Various acaricides have been investigated. Tetrachlorvinphos with dichlorvos was the most effective at treating chickens that were naturally infected with northern fowl mites, followed by carbaryl dust (Sevin), malathion dust and 10% garlic oil. Permethrin failed to reduce mite populations significantly. Ivermectin is also commonly used to treat mite infestations. It appears to be effective in poultry but only when combined with premises treatment. All of the above should be available at your local feed store. Please respond with further questions or concerns if you wish.