Most Intel BSPs are located under http://git.yoctoproject.org/cgit/cgit.cgi/meta-intel/tree/?h=daisy
However the Edison sources are currently handled differently.
I have however, started a thread attempting to get Intel to start participating in up-streaming to the yocto project:
Let's include Edison in the "Official layer for the Intel platform/board support"!
Currently, the Edison image src comes from https://communities.intel.com/docs/DOC-23242
which includes http://downloadmirror.intel.com/24389/eng/edison-src-rel1-maint-rel1-ww42-14.tgz
Those are the only official sources I'm aware of other than those.
For now I just dumped edision-src*ww42-14.tgz into https://github.com/instantinfrastructure/edison-src
Might want to take a look at the Intel® Edison BSP User Guide