The following may be of use to you: 
How to compose for shakuhachi - resource pages. Shakuhachi Chamber Music Composition Competition 
More info can be found at: 
Shakuhachi Forum - World Shakuhachi Discussion 
Approach the latter like a thrift/op shop or garage sale; lots of junk, some of it interesting, much of it not, and occasionally just what you want. You just need the patience to search through the clutter.