Why not try phoning the office staff at the school he attended giving them his details? It won't hurt to ask.
He may have to visit the school for them to check his identity before disclosing the details due to data protection laws - he might even have to apply in writing.
There isn't a common organisation which holds results details. If he knew the exam boards concerned it may be a start as he could contact them. The trouble is that if he can't remember the results, he's not likely to remember the exam boards concerned.
Let's hope he's not in a rush.