Install GCC for Mac? 10.5.8
May be you can find some binaries online but downloading XCode from Apple is really the best option (even if the file is a bit huge)
Your Mac installation disks have a version of XCode on them that you can install, though it's likely not as new as what you can download.
Without knowing what you need to compile bison for, I don't know if a system like homebrew is adequate or not, but it may be something you can look into.