There's only prograns like Quickpar and Smartpar that use .par files to correct .rar files. But the .par files are basically a small group of images of the .rar files. So say someone made an image of a CD, then rar'd it up into 20 different rars. They would have to make a small group of say 5 par files to be able to correct corrupt, or missing .rar files from that group.
But I'm sure you are just looking for something that can correct a corrupt one by assumption of file structure.
There is, as long as the person archiving the file selects "Put Recovery Record" before they run it. If you don't select that option and try to run the repair tool it will give you an error saying it couldn't find the recovery record.