Successfully complete the following tasks to get the corresponding weapon:

  Dragon's Claw and Tiger's Fang: In Chapter 4, take those weapons from the 
  glass display case in the first room at the Statue Of Liberty's base. 
  Eclipse Scythe: In Chapter 6, defeat Volf. 
  Falcon's Talons: In Chapter 2, you will see another building just before you 
  go to the Dragon Shrine. Kill the ninjas there. 
  Kasari-Gama: In Chapter 5, a dead ninja will be holding this weapon on the 
  second bridge you reach on your right. 
  Lunar Staff: In Chapter 1, there is a statue in a shrine holding that weapon 
  after the halfway point. 
  Tonfa: In Chapter 7, this weapon can be taken from a dead ninja in the storage 
  room that you drop into.