Try using the "hints" they give you on your tree, chances are that someone else has someone you know of (you grandparents) already on their tree, if you get lucky they might have more information than you do and you can work your way from there.

Another method would to be to identify a known Gambino mob member (and there are quite a few besides the famous Don Carlo) and maybe someone has a tree connecting them to people you know of in your family. And yes, I've checked and a user ( madeleinelopez) has Don Carlo on their tree.

Gambino should be relatively easy to track down because it's a rare name that comes from one region of Sicily. There's big cluster of Gaminos in California, New York and Philly according the quick search I did. If you were looking for a John Jones who you "think" might have been in New York, well that's a other ball of wax.