There are many places you can find market share data, including the following databases. They will typically provide market sizing information like "x industry is worth "y" amount of money" and/or share information like "x company has y % of the total market". You may want to create your own estimates tailored to your specific target audience.
Scroll to Market Share Reporter. This publication gives the market share of individual products and industries on a global scale. The breakdown varies depending on the product or industry.