I have found most of the ground textures and will be mucking about with them shortly, but there are no obvious candidates for the cause.
I'm excited about your project, Formaldehyde! I also like to play with ground textures in other games, and use Paintshop Pro to improve custom maps, etc. Here's one candidate for a texture mod:
Let's say you want to make a wintertime custom map, and you want the look of snow on the ground, but you don't want the constant snowflakes and blizzard-like conditions of the the LG "snow" weather effect and you don't want the streams/ponds to be automatically frozen. Could we have a "snowy" ground texture that has mottled snow and mud, etc., and then be able to use it on maps where we set the weather to "fog" or something else. This would be excellent for 1812 campaigns in Russia, and also for 1814 battles in France.