You as the biological parent will have to sign a form giving your permission for your husband to adopt. Your husband should file the petition to adopt, but you will need to do the work for the public notice first. If you do not know his whereabouts you may just have to post it in your county for thirty days. The best route for you to take is to call the Clerk of courts in your county and ask them what you need. They can help you out and let you know where to obtain the forms.
You will need a certified copy of a birth certificate of you, your son, and your husband. Because you do not know where your ex is, you adoption will take a little longer due to the thirty day notice, but after that you will have a smooth ride!
Julie
http://stepparent.adoptionblogs.com/