If everything fails, the only option left is to use a data recovery application which can scan and recover as much data as possible. Disk Warrior 4 is one such application which saved the day for me. You can either use a bootable DVD or create a bootable USB as shown below.
- Get your copy of Disk Warrior 4 and mount the .CDR image from Disk Utility from Mac Recovery.
- Partition a external USB pendrive to match the partition on mounted Disk Warrior image.