The G4HadronicProcessStore->GetInelasticCrossSectionPerIsotope and other associated functionalities are present in the Desy class reference system and in the source code, the actual functions in the code appears to be empty and thus cannot provide accurate and much needed information http://www-geant4.kek.jp/lxr/source/processes/hadronic/management/src/G4HadronicProcessStore.cc#L260 Shows the functions are empty. Either proposing a new method with which to extract isotope production cross sections or implementing the necessary functions would be greatly appreciated.
This is a deprecated method and soon to be phased out. Please see my answer to your HyperNews query 1515 in the hadronic section.