Any tool shop should have stock http://www.youtube.com/watch?v=_zBiZ0qvwVw

That's the external thread file covered, it's an infernal one which might be more difficult to find in a tool shop.

http://www.cromwell.co.uk/SHR0179020C

On a hub carrier which wasn't too badly mangled, I managed to clean up the thread with a tap of the correct pitch held in mole grips, but if the thread is heavily bruised, it may be beyond saving...

ken