Planar Warforged: Living constructs are nothing particularly new on the planes. One could make a compelling argument that the modrons are the oldest example of such a race, and a small number of similar creatures are known to exist in parts of the Planes of Law. None of these were specifically created to be war machines, however, and it’s seen as no small irony that primes seem to be the first to come up the idea. As it stands, while all warforged are native to Eberron, a slave trade has sprung up to transfer some to buyers in Acheron, Baator, and Mechanus. The Fraternity of Order, Sodkillers, and Baatezu are particular interested in learning the secrets of the warforged’s creation, but whatever force is responsible for bringing them to the planes seems to be more than capable of hampering such efforts. Still, it may be only a matter of time before planar versions of the constructs begin appearing.
Source: PSCS Releases, Chapter 2