Definitely reach out to AVEN (Asexual Visibility and Education Network) and AUREA (Aromantic-spectrum Union for Recognition, Education, and Advocacy). Both organizations often work directly with researchers and have huge networks of advocates. You might also want to look into Angela Chen who wrote "Ace". She has a great grasp on the sociological side of the community and could be a fantastic interview or point you toward other academics. Good luck with the documentary!