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It doesn't really make sense to compare, say, a 'widget trade show' with a trade show about 'whatchamacalits' because they might have zero audience overlap.
So it wouldn't really matter which was bigger, just which one was the biggest for the 'widgets' they are representing if that makes any sense.
Try a (insert favorite search engine url here) search for '{keyword} trade shows' and I'm sure you will find something.
Or perhaps somebody else has some better ideas?