Python's installation comes with some handy tools, located under 
$YOUR_PYTHON/Tools/Scripts. Is there a platform-independent way to find out where on a system they are located? I want to use ftpmirror.py as part of a shell script.
I see you are talking about the source bundle of Python, which includes Tools/Scripts, a set of helpful scripts for working with Python Source. It should be noted that they are not a part of Python Standard Library and installers are not obliged to bundle them with their distribution, for e.g in Ubuntu, I don't find it in /usr/lib/python2.6 or some other path.
If you want to rely on any of the Tools/Scripts, just carry them along with your script, that would be most portable.
Python: detecting install location of python tools