I suppose you could use one of those software hoarder sites. But, I would not. And, I do not see the point. Just be happy you are updated.
Also, read the announcement here: https://forums.intel.com/s/topic/0TO0P00000018NEWAY/desktop-boards
Getting a ROM/BIN file extracted from another identical board is not the way to go either. The flash component contains branding information -- Serial Number, MAC Address, etc. -- specific to this other board. Using this file on your board would thus make this board a clone of that board and this could cause problems. There are no user-accessible tools that would allow you to modify this branding. Bottom line, I strongly encourage folks to NOT make ROM images available to anyone. You would not be helping.
As for your situation, I suggest that you reattempt the BIOS update process using the BIOS Recovery process. I have it fully documented here: https://forums.intel.com/s/question/0D50P00004VhEOFSA3/how-to-upgrade-dz75ml45k-bios-from-0006-to-00....