It is surprising to hear that this part is not available given that your car is not particularly old or rare. We have no doubt you have tried many different companies to source a replacement, but we would suggest trying other Vauxhall dealers around the country, Vauxhall specialists, online parts specialists, breaker's yards, online auction sites or even Vauxhall owner clubs. You may also wish to try an independent Vauxhall specialist who may be able to fit a pattern part and extinguish the warning light to avoid the MoT failure.