Ted Nottingham offers a special presentation on key passages of the Gospel of Thomas, considered to be older than the four Gospels and source material for them. In these sayings of Jesus, lost to the world for two thousand years, we find a depth of wisdom and spiritual knowledge (gnosis) that is utterly transformational to those who would meditate on them and apply them to the moments of their lives.
I don't think God would allow any books to be "hidden" that He authored thru man. I believe the 66 books of the Bible are complete as God wanted us to have it and any others may be interesting but not necessary for our salvation.