There is no single resource for market share information.
Market share is calculated by dividing a company's sales over a period of time by the total sales in a given market or industry. This calculation is almost always determined by consulting various sources.
The best resources for examining secondary market share/brand share data include:
Click Industries within the menu bar. Next, select a tile (e.g. Home Products > Pet Care). Within the "EXPLORE ANALYSIS" box, select options to built your search including "Country Report," industry segment (e.g. Cat Food), and country.
Search for a known company or industry. Select an industry report. On the report page, locate "Major Companies" among the side-navigation tabs. Examine the breakdown of the Industry's market share.