I imagine those at http://www.thisislancashire.co.uk/ and http://www.lep.co.uk/ are the best to start with.

One snag is that by putting too much *visible* effort in, it might mean the person will ask a silly sum if/when you find them.

Did you try the DVLA? I am guessing that they would refuse disclosure unless you were to tell them porky pies about why you wanted the information (I would obviously not recommend this).

Gareth