I've been using this one for the past few months:http://tinyurl.com/nphp89j
(scroll down to see the listing details and picture)
Lots of different sellers seem to be selling it, expect to pay around £20.
Its been an absolute godsend and a pleasure to report some terrible van driving on the M53! There was a great one last week where a company van pulled out on me without indicating - driver giving all kinds of abuse for HIS mistake.
So I reported it to his company. Got the usual "sorry for this, out driver disputes your claim". So I send them the camera footage....