The starting point would be your own vet to make sure there isn't anything else obvious (head shaking along with scratching often indicates ear mites) and also generally you want your vet to make a referral to a neurologist though this isn't always necessary. Rod has a good list of neuros at cavalierhealth.org.
Thanks for all the feedback. I have decided to wait until after the Holidays and follow up with neurologist. Not sure if there is one in my state, my vet said they would get back with me about a referral.