I seem to recall a documentary about this boy a few years ago, and it rather concluded, without proof unfortunately, that he had been abducted by Romanies, in Greece.
As I understand genetics, its very unusual for a blue-eyed boy, to be the son of non-blue-eyed parents. Not impossible, just very rare.
As regards the blonde hair colouring, I was amazed to discover on a trip to Tunisia a few years ago, how many blonde-haired children we saw when we visited some Berber tribesmen. It was explained that it was down to the influence, 1000's of years ago, of Celtic traders !
Unless somebody is willing to spill some beans, I think it highly unlikely that he will ever be found again. This is terribly sad for his family, but after so many years, perhaps they will never find any peace.