That's definitely a good idea when the company operates only in the market you are interested in. However, it doesn't work when the company has multiple revenue

That's definitely a good idea when the company operates only in the market you are interested in. However, it doesn't work when the company has multiple revenue streams and doesn't break them out in their published accounts. In that case, if the company runs separate sites for each revenue stream, you can use Alexa (or similar) to get an idea of the traffic percentage to that sub-site and use it as a crude proxy for revenue.