A few thoughts, apart from reverse lookup....
1. Find out what they mean by "can't locate him." Do they mean they have no idea where he is, or that he just doesn't respond when they call/mail? If it's the latter, can he be served with any kind of papers? Can the state agency serve him? Around here, if you refuse to accept service of legal papers, the sheriff's office can serve you, and you get charged for it.
2. Who are your state representative/senator? Try hounding them.
3. If he works at all on a payroll, the state tax office has a record of him, and of who pays him. Why can't his wages just be garnished?
4. Have you called around yet to see who does pro bono work?
5. Something tells me Mike Huckabee's office is not big on deadbeat dads. If you can't get pro bono help, try calling Huckabee's office and explaining nicely about your situation and how you're looking for someone to do pro bono to catch a deadbeat dad and help him fulfill his family responsibilities, or, failing that, some way for the child-support division to track him down through taxes and garnish wages.