Many people hear about the book of Enoch, and other Apocryphal or Pseudepigraphal works that have no idea where to get them.
Thanks to Biblical Studies Online, I have found this source that gathers most of the writings that didn’t make it into the Old Testament. It is the Apocrypha and Pseudepigrapha of the Old Testament in English by Robert Henry Charles. It can be found in the Christian Classics Ethereal Library (CCEL).
Now you can go and read the two books quoted by Jude, The Book of Enoch and The Assumption of Moses.