Are there any parts of Tolkiens books that outline in more detail the populations and life East of Rhun? I have seen differences in locations of cities and towns around the Sea of Rhun itself, as well as an Island in the centre that sometimes is omitted in other maps.. I'm wanting to know what is the best and most detailed description of this part of middle earth.
I can find very little. Tolkien devotes a small amount of space to describing the "uttermost East" in "The Hiding of Valinor", which was published in The History of Middle-Earth I: The Book of Lost Tales Part 1 (emphasis mine):
Wherefore said some [of the assembled Elves, Valar, and Maiar]: "Let us send now messengers to discover the fashion of the world in the uttermost East beyond even the sight of Manwë from the Mountain of the World." Then arose Oromë: "That I can tell you, for I have seen. In the East beyond the tumbled lands there is a silent beach and a dark and empty sea."