Omigosh - this is so much along the lines of my biggest genealogy moment!
My husband was a love child - he was adopted out and his birth father was killed climbing the Himalayas a couple of years later, in the late 60s.
It took years, but we found his birth father's family - none of the siblings had known there was a baby.
Last summer, we took our family to Australia to meet his uncles and aunts and cousins. It was amazing! So worth all the energy spent trying to locate the family.
I wish the family luck - someone somewhere knows who is who, and the local newspaper probably is the best way to reach them.