Clan War has a number of models that can be used for Okko.
They've finally gotten around to making the skeleton and zombie troops available again. Which would work well for the undead in the Kerasu Expansion.
http://www.veltd.net/28mmshadowland.htm
Clan war also has some really good ninja with kusari gama chain weapons, unfortunately they aren't available unless you can find them on ebay.
Perry miniatures also has a great line of Ninja, Monks and Samurai
Villager set has a komuso monk.
http://www.perry-miniatures.com/product_info.php?cPath=23_38&products_id=2348
http://www.perry-miniatures.com/product_info.php?cPath=23_38&products_id=2337
http://www.perry-miniatures.com/product_info.php?cPath=23_38&products_id=2350