There really isn't any magic to it. To get the data someone has to do the Primary Research (Grunt Work). It's either in a report that an agency has put together which you can purchase (Good ones are expensive), or you open up the marketers best friend, Excel, and start collecting data.
Last year my co-founder and I spent a good month basically doing data entry trying to quantify our target market. I'm very confident that no one knows as much about it as we do now. It's hard work, but it's worth it.
Just keep your scope and data points the same across everything you're quantifying otherwise the data is useless. Check the same months in the same years, use the same tool (Compete, Alexa, etc. all report different numbers, we stick with Compete which generally underreports actual traffic but it's consistent).
Last year my co-founder and I spent a good month basically doing data entry trying to quantify our target market. I'm very confident that no one knows as much about it as we do now. It's hard work, but it's worth it.
Just keep your scope and data points the same across everything you're quantifying otherwise the data is useless. Check the same months in the same years, use the same tool (Compete, Alexa, etc. all report different numbers, we stick with Compete which generally underreports actual traffic but it's consistent).