On the College of Optometrists in Vision Development/COVD website, there is a "Locate a Doctor" tool. You can search by zip code (see box on left side of page) or by city and/or state, you must first select a country. COVD is the certifying body for doctors in the optometric specialty called Behavioral/Developmental Rehabilitative Optometry. It is important that you like your vision therapist, as this will hopefully be a long relationship, so like any doctor, pick someone you feel comfortable with.
Good-luck and work hard!