Call me thick
but how do you assess how many are actually left....for instance..I put in Vauxhall Omega, and the results give figures for various Elites for example.
Elite V6, Elite 2.5, Elite Auto.....confusing 
The database covers all vehicles that have a valid tax disc or a Statutory Off Road Notification (SORN). It doesn't cover cars that were off the road prior to the introduction of SORN, or cars that have never been registered on the road since manufacture.
If you can't find your car, it doesn't mean that the DVLA thinks it doesn't exist!
Most vehicles are listed under the make and model recorded on their V5 documents. In some cases though, the make and model name isn't properly recorded and the the vehicle will be counted under one of the following alternative categories:
Another similar model from the same manufacturer. eg. The author's Subaru Legacy GT-B is counted as a Subaru Legacy, because the GT-B is a Japanese model that was never sold in the UK.
The 'Missing' model from the same manufacturer. eg. A Bugatti Veyron is counted as a 'Bugatti - Missing', because the Veyron model hasn't been registered on the DVLA database.
An 'Other' make and model. eg. A Pagani Zonda is counted as an 'Other Italian - Missing', because the Pagani make hasn't been registered on the DVLA database.