I always felt Monk Weapons were rather silly.
Personally, I think Shuriken should just follow the rules of throwing knives, Siangham is basically a crappy dagger, Kama is a Sickle, etc...
The thing is, most, if not all of the Monk Weapons are already in existence as another weapon that's not only historically similar or identical, but has identical stats aside from the fact that one is a 'Monk Weapon'
Sickle=Kama (Kama is a Japanese Sickle...)
Nunchaku=Light Flail
Etc.
I personally feel Monks should be able to use Simple Melee weapons with all of those options, since they pretty much cover the exact same gap, and then they'd get to use spears, which real Shaolin and Wudan monks actually train with.
But then again, personally, I don't think they need 'Asian' weapons or classes, when most of what is in the base book and the non-monk weapons all fit an 'Asian' setting perfectly.
Samurai=Fighter, maybe Paladin
Ninja=Rogue