Does the LEND database do any better? Or is the lack of isomer awareness in the PhotonNuclear process itself, rather than in the model/database?
For LEND, the data comes from ftp://gdo-nuclear.ucllnl.org/LEND_GND1.3/LEND_GND1.3_ENDF.BVII.1.tar.gz . After unpacking, set the $G4LENDDATA envvar to point to the directory (full path). This is not done automatically by either the G4 installation or the geant4.sh and related setup scripts.