Publishers

Some publishers produce reprints of older books relating to India, or books in respect of specialised topics such as military.

Naval and Military Press

Its website says that its range of books covers the whole spectrum of military history with titles on uniforms, battles, official and regimental histories, specialist works containing medal rolls and casualties lists as well as titles for genealogists, medal collectors and researchers.
An example of one of its books is "The East India Company's Arsenals & Manufactories" by Brig-Gen Henry A. Young, Director of Ordnance Factories in India 1917-1920, first published in 1937 and re-published by Naval & Military Press in 2005 which gives historical background of munitions factories etc.
Also see Military reading list

Leonaur

Its website says Leonaur is dedicated to publishing hard to find and rare books at prices that are no greater than those of popular, mass market titles. Its books on Military History include titles relating to India. An example is Galloping guns : the experiences of an officer of the Bengal Horse Artillery during the Second Maratha War 1804-05 by James Young which is described in this link Also see Military reading list#Other wars and battles