if there is a torrent of the original file, you could join the torrent and select your bad hash file as a partial file. then the torrent program would scan your file and redownload the bad chunks... (and since you have three files, you would load up all of them , perhapse in three different clients or pc's? ,and then join the torrent, it might be that you have a complete file out of your three downloads)
this also would work on the edonkey p2p network , i think...
also there is a freeware program called 'zidrav'. so if you know of someone else that downloaded the file, you both run zidrav and you send him the checksum and he sends you a 'patch'
ZIDRAV is a file corruption detection and repair program. It's designed to provide a way to fix file damage without having to redownload the entire (potentially large) file over a (potentially slow) connection.
http://sourceforge.net/projects/zidrav-- i bet this program could be advanced with a nice gui and perhapse some internet support/automation, if any programmers want to take a crack at it--
but yeah, interesting problem and good luck!