I don't know about English website. But each competition is held by some organization, usually called sort of agricultural association. They always publish all winner's names (most of them are not company names, as most of the best tea are grown by unincorporated farmers).
But then, if you don't buy directly from the farmer, it's hard to track. But if you by units in 300g (sometimes 600g or 150g), you should get a standard jar with track number to look up in the relevant organization's website (probably no English website though).
I agree with edkrueger that few people would lie about competition tea (but of course anything could happen especially if it's something like the champion...) as competition teas are not necessarily expensive or the best (usually decent though).