Try searhing in genesreuinted.com.au. I located who my grandfather was in that site just over a year ago. My grandmother married 3 times and I had no idea who he was.
All I did was put a message on there saying who I was, who my father was (I didn't realise I had the surname wrong at the time - he was adopted at 9yrs by his stepfather), his mothers names and my great grandparents names. I wasn't expecting any replies and the next morning received very helpful information. So good luck and be patient.