The New York Public Library has a large collection of color plates of the armies of Finland in the 18th and early 19th centuries.
Here’s a large selection of color plates of the uniforms of Norway and Sweden from 1500 – 1909.
The New York Public Library has an online collection of color plates of Egyptian uniforms for the period 1820 – 1898. This should be a great reference for people interested in the Sudan and other North African campaigns in which Egyptians participated.
The New York Public Library’s Digital Gallery has color plates of German military uniforms dating from 1740 – 1900. These include the uniforms of German states such as Anhalt, Bavaria, Saxony, Hamburg, Hessen, Prussia, Nurnburg, Saxe-Weimar, Wurtemburg, and Westphalia.
For a terrific collection of color plates of French military costume from the Gauls to 1806, visit The New York Public Library digital galleries.