I've got an 07 plate 159 and have had to change the front one. Unfortunately the only way seemed to be buying the whole chrome surround with badge, at around £35-40!
Then the nice men at Simply Alfa took the old one off, was a paper thin metal stick on job, then replaced it with another, bit of double sided tape, bingo.
Bit worrying though, 2 and a half years old and needs a new badge.