You can see some of these darts in the fifth picture down in this article:
http://chinesemartialstudies.com/201...partment-1925/
My suspicion is that they aren't often collected because the more modern examples were gang weapons. In Japan, there were small schools of shuriken-jitsu, and the older examples seem to have been passed from teacher to disciple. It's unclear that this happened in China.
Incidentally, there are a several of the precursors to the Fairbairn-Sykes knife in the seventh picture down.
F