I am doing some Fortran 77 stuff on Red Hat Linux 6.0. gcc wouldn't compile my f77 code and gave me the error that it couldn't find f771 to exec it. I found the file in /usr/lib/gcc-lib/i486-linux/2.7.2.3. Once I copied f771 from there to /usr/bin, the problem was solved. (More specifically, I encountered the problem while compiling a numerical analysis package named PETSc. More info on this from http://www-fp.mcs.anl.gov/petsc/
Red Hat Linux 6.0 and later does not ship with fort77 anymore. You will need to recompile that package from the source rpm (or use the one in powertools) to get it woring right You might also use the g77 compiler that comes with egcs in Red Hat Linux 6.0