We forgot to ask you what file system you're using for the storage drive. From the utilities you're using, I assume it's NTFS.
As long as you've got your hex editor out, look at the documentation for the FLAC file format and see if there's a pattern to the corrupted bytes (for example, 4C is often missing but the other bytes are correct in the identifier). If you can find a pattern for the damage, running a replace operation might work for at least those files that match the pattern. It's a long shot, but if they're really important files (I hope they're not) it might be worth the time and effort if your forensic utilities can't help.
On the other hand, your time might be better spent scouring eBay or your local thrift shops/used CD stores for replacements. Used CDs, as you know, are very cheap these days. You haven't told us what's in the files you're trying to recover, so I'm just assuming they're either commercial music or legally circulating live shows.
As long as you've got your hex editor out, look at the documentation for the FLAC file format and see if there's a pattern to the corrupted bytes (for example, 4C is often missing but the other bytes are correct in the identifier). If you can find a pattern for the damage, running a replace operation might work for at least those files that match the pattern. It's a long shot, but if they're really important files (I hope they're not) it might be worth the time and effort if your forensic utilities can't help.
On the other hand, your time might be better spent scouring eBay or your local thrift shops/used CD stores for replacements. Used CDs, as you know, are very cheap these days. You haven't told us what's in the files you're trying to recover, so I'm just assuming they're either commercial music or legally circulating live shows.