You should be able to get one easily from your nearest dealer. However, that is usually the most costly option.
If you are watching the price, then you could go to a breakers yard that deals with newer cars. There are many that that take cars involved in motorway accidents and they include many younger cars - there is one at Redbourne in Beds for example.
If you look in your Yellow Pages there are many vehicle dismantlers who are part of a nationwide parts delivery scheme. You simply state what part you want and dealers who have the part contact you with the price of the part and delivery. Hope that helps.