Help Save International Adoption by Signing this White House Petition

On behalf of my mum, I'm looking for a son, who was born in February 1971 at Bethany in Auckland NZ. His birth name was Brenton Robertson, birth mother is Barbara.
He was adopted at birth and move to AU not long afterwards, with his adoptive parents, who were in their 30's.
No other information is at hand at present.
Any and all leads would be greatly appreciated.