I'm afraid they are basically lost then.
Once new photos are taken the camera over writes over old deleted data.
I've used the Recuva software when accidently deleting photos and it was able to recover photos but I didn't take any new photos once I realized my mistake.
There are data recovery specialists out there that might be able to recover something but they charge a fair amount and with new photos written over top there may only be a certain amount recovered or only partial file recovery.
I have a photographic memory, trouble is most times the lens cap is on.