Hi mate,
If you find out, let us know.
Unfortunately, my wife hit a dog a few months back (it didn't survive - she was very shaken, and being dog people we both took it pretty hard...)
The collision took off the undertray and the mudgard things you mentioned - so I'm missing one of them now (the undertray was refitted no problems). Not sure what they're for, but I do like things to be present and correct in my car.
Cheers,
A.