You'll probably have to go to a main dealer for it. I doubt an average car accessory shop will even know what you want and less likely to stock one as they are different from one car to the next.

I had to go through a few parts shops and garages, but I did find a chap at a shop that knew what I wanted and ordered it for me. It's all sorted now.

Next time I break something on my car I'll make sure it's something a bit more mainstream!