Good Morning---
While I do not know the correct answer, I wish you lots of luck. It sounds like your dh just wants to find the rest of his family. If you know where the mother was when the baby was born, perhaps your dh and his nieces/nephews, could leave letters of their interest in finding him. If you know his name, look on Facebook too. Don't give up, however. In our small town, a mature (40-50) year old adoptee just found her family last year. Again, good luck to your dh and his family...all of them!