1) Talk to him sincerely. If you let him know any more from him goes to your child not to reduce your responsibility, he will give in and consult with you. Anyway your son is also his.
2) Let lawyer take the legal route to demand for the info, if you have a lawyer to help. The lawyer can use teh attorney previlage and press for the info.
3) If you represents your self, you can use the court to demand for the information.
希望所有的夫婦和ex-夫婦都能好說, 好散, 好商量.