Medicine Woman,
Pre-Biblical and Pre-Flood don't have to be the same thing. The flood wasn't the first story in the Bible.
But as far as Nephilim in pre-Biblical books goes...None that I know of.
But there is debate as to what the Nephilim were (In the Biblical stories, of course) Most Bibles change the word "Nephilim" to "Giants." But because of the uncertainty of this translation, some Bibles have left the word "Nephilim" in the text, untranslated.
Zackariah Sitchin, whom isn't the most credible scholar in the world, actually translated the word into "Those who have come down from above." The biggest problem in figuring out what exactly the Nephilim were supposed to be lies in thier parents.
They were said to be the offspring of the "Sons of God" and the "Daughters of Man."
But how could the Sons of God be human? The most famous Son of God is Jesus, and he was, as far as the Bible says, was God himself. And if the Sons and Daughters lineage is clearly divided by the "Man/God" monikers, then what, exactly, were the Sons of God?
Some say angels, some say deamons in human form, some say Nobles and Kings.
So, to answer your question, the problem with finding Nephilim in anything other than the Bible is the fact that we are no more clear as to what the Nephilim were than we were when we first began translating the texts.
JD