Battletech how has their SLDF Field Manual available as either a pre-order for the print copy or as a .pdf from the website.
From the update:
Field Manual: SLDF describes the single greatest military force the Inner Sphere has ever seen: the Star League Defense Force. Including a brief history and overview of the SLDF, its formation, organization, and training programs, this book provides the most detailed look ever at the army that protected the Inner Sphere before the treachery of Stefan Amaris and the Succession Wars that soon followed. Special rules are also included, enabling players to create Star League forces for use in campaigns set in one of BattleTech’s most storied eras.