Perhaps you did not notice that, besides Cain and Abel (who was murdered), Adam and Eve then had another son called Seth, and Noah's line of descent came through Seth, not Cain. 1 Chronicles 1:1 states, "The descendants of Adam were Seth, Enosh, Kenan, Mahalalel, Jared, Enoch, Methuselah, Lamech, and Noah."
Have a read of Genesis 5:3-32.
Cain's descendants are mentioned in Genesis 4:17-26 and also that Seth was born later to Adam and Eve, who fathered Enosh and all the way down to Noah. Perhaps confusion comes with thinking the Lamech mentioned in chapter 4, having Cain as his great-great-great-great-great-grandfathe... is the same Lamech mentioned in chapter 5. However, THAT Lamech had Methusela as his father, whereas the Lamech of chapter 4 had Methushael as his father.
I think that clears the misunderstanding up. There is no list of descendants from Cain after the flood.