think its under boot lid.. if yuou cant find it just ring up local fiat dealer give your reg in and they should give it too you over the phone.. thats what i had to do when i needed mine
It is located on the left hand side of the boot lid, or if your a dunce like me and didn't see it just give fiat a ring or drop them an email with the Reg plate they will be able to help you.
But just as a note due to the colour fading overtime the colour you get made may be a tiny bit darker as it was with mine but still a damn good match