Standard gaitor as there is nothing out there thatwill fit really.
The problems that you will encounter:
1) Putting car into reverse, the gaitor gets trapped and you have to move it
2) You end up pulling it out of the clips as its too long
3) looks too big for it
SO failing that i decided to mess with it since there quite cheap.
Remove from the car and undo the staples which hold it to the plastic surround.
trim away how much you need to remove (dont go too mad or it wont fit back)
Then re apply to the surround and replace with new staples (strong ind ones)
Now you should be left with a shorter surround, which should pop back in ok.
If not get yourself to the dealers and buy a new one for about £5