I don't know of any free software that will work for this. I'd try a Google search for "file recovery." But if it's valuable enough to recover, and it might happen again, then maybe it's worthwhile to pay for the software. If you buy a pro lexar or SanDisk memory card, file recovery software is included. That's how I got mine. And I have used it a couple of times. One of those times made it worth the money and effort.

There's also a sticky thread about file recovery on the help Files forum. It's possible someone had listed a free program there: What if you lost your digital images?