Here, it is a multiplayer mod (has single player) but it has guns just for the player, and troops dont use them-
http://www.mbrepository.com/file.php?id=2407
I dont know how to upload, but a multiplayer mod called 1866 has it- http://www.mbrepository.com/file.php?id=2327 (it has no singleplayer available, from my version i didnt get any pathces from it so it might have sp in a patch)
Also blood and steel has guns- http://www.mbrepository.com/file.php?id=2119 (If you click ctrl + ~ on the campaign map you will get a line pop up type in "cheatmenu" click on camp and in the options there will be cheat menu option click it and then click find items go to the last array of items and there is a gun called cheaters cannon and cheaters cannon ammo get those and you will be able to shoot the cannon (with exploding ammo when it hits the ground) really fast, by the click of a mouse there will be a explosion where your aiming reticle is and everyone nearbye dies, and no other troop has that cannon but rhodoks have small weak guns and merceneries have really slow cannons.) So hope that helped.