I'm looking for the proverbial needle in a heystack..
Due to my own fault I've lost an encryption key

I thought I had backed up everything when I reinstalled my server. Unfortunately later on I realized I forgot 1 64 byte file.. DOH!

The old layout of the disk had 3 slices on it (fbsd), now there's only 2. I need to find that key that used to reside in a partition inside one of the 'old' slices.

I've looked at sleuthkit/autopsy but that seems to concentrate on analyzing the current filesystem, hence I can't find it.
Tried a few windows(!) programs too but none seem to be able to find it..

I know the file's name and I know it's size, how do I go about scanning the disk looking for that info?

Preferably I'd like something that scans the whole disk looking for past info on files that are 64 bytes in size.

The filesystem is UFS2 (Freebsd). Any hints/tips are welcome.