Go to the council and ask to see the electoral roll. They will only be able to show you the people that have opted in tho. Or check the phone book. Or hire a private investigator. Or go to a database company and see if you can buy that record off them. Other than that - camp outside!!
it would cause urther rifts and problems if you tried to do this in a covert way, if you are estranged from the mother but you are the natural/legal father of the child, have you applied to the courts for access? I think in the long term it would be better to use the recognised legal route, and if finance is an issue, you can apply for fee remission at the court.