I use AON and they accepted my purchase price from a few months prior to switching to a classic car policy ... up to that point it had been on standard insurance as my only car with Norwich Union and was my daily driver.

If you still have the paperwork from when you purchased the car if it wasn't that long ago ... maybe that ... along with a couple of adverts from AutoTrader (probably better to list 'trade' ads) might help??

Worth a try?