What are all these Orcs making way for? Why, its Athrabeth's new episoden orc-course! Ever wanted to know about how Orcs came to be? So did Tolkien! Find out what all the confusion was orc-bout!
J.R.R. Tolkien, Christopher Tolkien (ed.), The Book of Lost Tales Part Two
J.R.R. Tolkien, Christopher Tolkien (ed.), The Shaping of Middle-earth
J.R.R. Tolkien, Christopher Tolkien (ed.), The Lost Road and Other Writings
J.R.R. Tolkien, Christopher Tolkien (ed.), Morgoth's Ring
J.R.R. Tolkien, Christopher Tolkien (ed.), Unfinished Tales
https://www.amazon.com/Tolkien-Race-Cultural-History-Fairies/dp/0230272843