Hi dualer,
It's a great topic, and close to my heart!
You mention you have all the relevant Ospreys. I imagine those include:
*The North-West Frontier
*Indian Infantry Regiments 1860-1914
*Bengal Cavalry Regiments 1857-1914
*The British Army on Campaign (3) 1856-1881
*Queen Victoria's Highlanders
*Queen Victoria's Commanders
The closest thing to a "definitive" uniform reference I'm aware of for Bengal, Bombay, and Madras units in the Second Afghan War, and Indian Army units in the Third Afghan War, is the 2-volume history by C.Y. Carman, "INDIAN ARMY UNIFORMS." It covers the uniform history of just about every single regiment in the 3 Presidency armies, plus the Punjab Frontier Force, as well as the armies of various Princely States, from the 18th Century all the way to 1947. VOLUME ONE covers Artillery, Engineers (including Sappers & Miners and Pioneers), and Infantry; VOLUME TWO covers Cavalry.
The problem with Carman is -- in addition to not being cheap -- the portion of these books relating to Afghan War "field service dress" is pretty slim, compared to their overall page count. Some units have more information on their uniforms from earlier or later periods, or more information on dress uniforms, as opposed to what they wore on campaign. But, if you want access to at least some uniform info on virtually every Indian regiment that served in all three Anglo-Afghan wars, it's really the only title I know of that fits the bill.
When it comes to British uniforms, it's a bit easier. First, there were far fewer British regiments than Indian ones that served in these wars, so there's simply less information you have to track down. Second, most of the British units have written and/or visual datails of what they wore definitively recorded somewhere.
The closest thing I know of to a complete one-volume record of British unit uniforms during the Second Afghan War is the Osprey book, "British Army on Campaign (3) 1856-1881, which you may already own.
Here's a LINK to a comprehensive list of all British and Indian regiments that served in the Second Afghan War, courtesy of Garen Ewing's excellent web-site devoted to the conflict:
http://www.garenewing.co.uk/angloafghanwar/waroffice/regiments.phpThe above web-page includes each British and Indian regiment's Battle Honours awarded for the campaign, so is a good resource for checking if a particular regiment was at a particular battle.
I'm going to list some more books. My apologies if it's information overload, but one or more may be of some use to you, or another LAFer...
There are many general histories of the Anglo-Indian Army, and the North-West Frontier, which include some photos or artwork, or written descriptions of uniforms of various Indian regiments during the 2nd and 3rd Afghan Wars. These include:
*The Indian Army, by Boris Mollo
*The Indian Army, by Terence Heathcote
*The Indian Army of the Empress, by Alan Harfield
*The North-West Frontier, by Michael Barthorp
*The Sword of the Raj, by Roger Beaumont
Two other books I think deserve special mention for visual reference value are:
*The Army in India, a photographic record 1850-1914, Published by The National Army Museum
And...
*An Assemblage of Indian Army Soldiers & Uniforms from the original paintings by the late Chater Paul Chater, written and edited by Michael Glover
Finally, one other title I'd recommend, with visual uniform info for some British and Indian regiments in the Second Afghan War is:
*William Simpson's Afghanistan: Travels of a Special Artist and Antiquarian during the Second Afghan War, 1878-1879, edited by Peter Harrington