You can get that file from here
, it also includes adb, fastboot and drivers. It just needs to be placed in the same folder as your current fastboot/adb files.
I think there is a recent fastboot and adb update recently too, might even be required for 4.0.4+ ROMs. If this is the case, setup the android SDK (look for the rooting guide) and let it install/update platform-tools.
Device: Galaxy Nexus i9250
Previously: Nexus S i9023