With the map question firmly answered, I was wondering where I might read more about some of the different Easterling/Khand tribes in an ICE book.
Frankly, the ICE books had not much in them, as Easterlings were never a focus in any of them. And what little they had, it was always the "steppe nomad" stereotype. Ironically, all the Easterlings we read something of in some depth (the Wainriders and the Balchoth) were expressively
no steppe nomads, which makes the MERP choice highly questionable even for back then (at least if fidelity to the source is of any relevance).
I found the MERP fandom site has a good article and a list of MERP books that mention Harad (and Khand): https://merp.fandom.com/wiki/Category:Near-Harad .
Similarly, the MERP Fandom site gives a good summary of the history of Near-Rhun, together with a list of Merp Modules that deal with it: https://merp.fandom.com/wiki/Near-Rh%C3%BBn
Almost all of it is assembled from either MERP, original material and other fan sources. I know this guy from earlier times and he is a fan of these cultures beyond Tolkien's map. MERP's treatment of "Easterlings" is peripheral in some modules, but IMO it lacks a coherent approach based on the original source. The "Inland Sea" (see below) would have been a good first step, but even that failed to materialize due to the foundering of the old ICE.
They had some books on the Far South, but nothing on Near Harad. That was planned as well, but came to naught like so many other ideas back then.
On the latter site, there is even a Fenlonian close-in map of the SW shore of the Sea of Rhun, which I don't think I had seen before.
Oh, that is a nice colorization of my Rhovanion map (at least part of it). The whole file (in B/W) can be found on the OM Facebook site (see my signature for a link). This map is based on the unpublished MERP manuscript for the Inland Sea annd later published as a fan-product of the same name. It is good, though it shares MERP's deficiencies (naturally, due to its origin).
Best
Tolwen