The Riddle of Steel has awesome mechanics for running chanbara combat, especially if you get The Flower of Battle. Too bad it's really damn hard to get.

Two unarmored men with katanas facing off and trying to out-draw the other (stealing/buying initiative in TROS) is going to end up with one of them losing a limb or getting killed, pretty much every time. Fighting is all about tactics and choosing the right tricks at the right times, and for unarmored combatants, it's terribly dangerous. For armored combatants (plenty of those in Kurosawa movies), it's only really dangerous...

As an extra bonus, TROS has a mechanic where, if neither combatant is willing to make the first move (e.g. they're both waiting for their opponent to attack so that they can parry and counter, killing the attacker; cf. Kyuzo's duel in Seven Samurai), they can use the Intimidate skill to try to force their opponent into making the first move... perfect for samurai showdowns.


There's also Sengoku, which is a pretty good RPG, but nothing spectacular.


Aside: samurai movies and spaghetti westerns had a weird relationship. The whole samurai movie genre was sort of inspired by early westerns (lone wanderers, etc.; there's even a gunslinger in Yojimbo), but then several westerns were made directly ripping off samurai movies (A Fistfull of Dollars, The Magnificent Seven), and then they got even weirder by just combining them (Red Sun), and then it just got postmodern with Sukiyaki Western Django...