If he has abandoned this child in your care and not shown her any interest you can gain full guardianship of her through the court system by doing a few things that your attorney should know about...confused about this for sure...maybe I'm not understanding.
Anyway, if he has abandoned her and you can prove this then you don't have to do any more. All you have to do is run an add in the newspaper in the area he is supposed to be living in that states you are doing the court hearing and are going for guardianship of this child. That is legally enough since the child support enforcement people have been unable to find him too.
This shows he is gone and has no interest in this child.
Your attorney should know this though. That's why I'm confused. It's the law. When a child is left with someone for an extended amount of time and does not have contact or any support from either parent then they are deemed abandoned and someone has to step in and take responsibility for this child. There are usually cut and dry methods for dealing with this.
PS, as far as I know legally they are not ever supposed to hand anyone's private information to you for any reason. If they have a court order they can of course but many people take off to hide from abusive ex's so it's pretty much a no no to give you his address of record. They should not have done that.
When I need to get hold of one of the parents regarding child support of my grand kids I have to contact child support and ask them if they can send them a letter about. It's a strict breach of confidentiality to give out personal information to someone else, especially in these times when just about anything can be found online.