Here you go, I looked it up for you.
I think this is the part you need:
RealOEM.com * BMW E63 M6 Shield,engine compartm./underfloor panel
BMW Parts and Accessories | GetBMWParts.com
But do your own homework to make sure it is the right part for you as it differs if you have manual transmission or SMG and what year model.
Great post Dan in 2011. As I personally need this part now for my SMG M5. Came back from bimmerfest east 2015 yesterday heard a tapping/flapping noise looked under and shield was all hanging a bit and torn up some. Will order this part now, as I couldn't figure out the part # nor name until I found your post.