How much trim do you need? Just one piece? If so try
www.partsauction.co.uk (when it's back up - probably during the day tomorrow). It has new genuine parts at prices much lower than a dealer. Problem is it's luck of the draw to whether or not they have the part.
Failing that, if it is just one piece you need, the dealer can supply it - it should be a fairly reasonable price. Get a quote a least - it's often the case that bits like this on ebay go for more than it costs from a dealer!