The link http://spaceflight.nasa.gov/realdata/sightings/SSapplications/Post/JavaSSOP/orbit/ISS/SVPOST.html
is where we get our data from. Right from the NASA/USAF source at JSC.

The http://www.celestrak.com/NORAD/elements/stations.txt set can be a bit dated, specially after any maneuvers. But as a whole they should almost show the same location. Both Aus-City and Celestrak get the TLE data from the same source USSPACECOM. But we grab the data a few more times a day, every six hours.