I used

httrack  --mirror --continue +http://programmedlessons.org/*
<http://programmedlessons.org/>

but there were some 404 errors

turns out it  has files missing
those files are available at this original mirror
  <http://chortle.ccsu.edu/>

how do I tell httrack to look for 404's on this other mirror, i really don't
want to hit them up again, its kind of big (250+mb)

Thank you