Aside from the official three "mods" that come with the game (Napoleonic War, WW1, Space War) there are no others.

where do I find these "mods"

To see how the uniforms/characters look you can go to character customisation: In the main menu select "Profile" -> "Uniform". On the left side you can see the Union and Confederate flag and above these you see "Civil War", if you click that you can select the various mods and see how the characters look and change a few things (but of course not as much as you can customize your Civil War characters.

To actually play one of the mods that come with the game you need to either find a server that runs the mods (for example look for "BCoF Napoleonic Commander Conquest" and select that if you want to give the Napoleonic War mod a try) or download the dedicated server for BCoF and open your own server, setting the "era" to the respective mod you want to play. Only the Civil War base game and the Napoleonic War mod are really worth playing though in my humble opinion (that is also the reason why there are practically zero other servers running space or ww1).

Hope that helps.

Thanks DMW

Glad I was able to help mate! :)