The latest source code for the photon compiler can be found on the Photon repo on github under the branch 'ometa-compiler'. The version on the repo is not buildable because the d8-tachyon-exts.cc must be accomodated and I still need to discuss this with Maxime.
Anyway, the source code for the object model in C is 'bootstrap/photon.c'. The ometa compiler is 'ometa/photon-compiler.txt'. The supporting photon library is 'photon-lib.js'.
Erick