An incredible Russian site with thousands of quality illustrations. Large selection of portraits with bios (Russian) much on uniforms. Google translate works well for those that do not read Russian. Truly a labour of love.

http://impereur.blogspot.com/

On right side is list of subjects covered, most by country. Click on images to enlarge.

Many interesting items, just one of these:

Japanese wood cut prints of Russian uniforms (1804):

http://impereur.blogspot.com/2014/03/1764-1807.html