I'm afraid I'm unaware of any software that does this, but if you find it, I might take a copy.
When you say unused drivers, how do you mean exactly?
Used drivers can be identified because they are linked to the hardware item in the REGISTRY. Unused drivers do not have links anywhere (that I am aware of), and so the computer would not know what file is a driver that is not being used.
The software would have to scan EVERY FILE on your PC (like Norton AV would) and then cross check the name and version etc against a database of known drivers...
I doubt that it exists.
If you want to get rid of a driver that is not being used, then just delete the file. Of course you need to make sure that the file is not going to be needed at any point in the future.