"My people were perfecting the arts of crafting and fighting with swords when your kind were still living in primitive huts, savage."
You can recruit foreign troops in FotS, so why not in good ol' Sengoku Jidai? These mercenaries have superior defense to Samurai, but less attack and morale. The changdao troops don't hit as hard as no-dachi, but have a decent anti-cavalry bonus.
Both are recruited from the same structures as their Japanese equivalents, but require a trade port.
I wanted to due Joseon (Korean) cavalry mercenaries that would have low armor but better charge than Great Guard, but there simply aren't any skins in the game that can remotely pass for Korean clothing/armor.