With the collapse of the Soviet Union, a wealth of new material on the old Imperial Army began to come out of Russia. Most are available from dealers in the UK, Russia, or the US. One very good source is Atlantic Crossroads, Inc (
www.collectrussia.com) which also carries books on Imperial Russian Orders and decorations.
As a student of military uniform, I would recommend the following, which are currently available:
"Russian Imperial Guard" by Gerard Gorokhoff - A superb photographic record of the regiments of the Guard from 1894 to 1917. It has a number of photographs of members of the Imperial Family with their Guards regiments. It is in English and Russian.
"Russian Line Infantry 1801-1855" by Leonov and Ulyanov - Magnificent work detailing the uniforms and colours (flags) of the line infantry regiments in wonderful color illustrations. A companion volume detailing the uniforms and colours from 1855 to 1918 is also available. The text is in Russian.
"Russian Guard Cavalry 1914-1917" by Deryabin and Dzys - Text in Russian, but color plates and photographs are worth the price.
"Russian Junkers" by A. Vorob'yova - An excellent treatment of the Russian cadet schools during the monarchy. Text in Russian. Color plates and B/W photos.
"Banners and Standards of the Russian Imperial Army of the late XIX-Early XX Century" - Text in Russian. Excellent color plates and photographs of the flags. The book, together with an English translation of the text can be obtained from Gauntlet Publications (it is on the web).
There are other excellent books out there, but these ought to whet your appetite.
W.L. McCaughey