If it's that important you could try something like this, or a data recovery service may be able to do it for you. I'm not aware of any free (or even cheap) utilities to do this.
You could always download the trial version to check; it won't recover anything but it will tell you whether it can or not.
The crucial thing is not to write a single byte more to your harddrive. Each time you write anything, you risk overwriting data necessary to decrypt the data (if that hasn't happend already).