Search the Web of Science Core Collection for your topic of interest and use the Analyze Results tool to determine which funding agencies are in that space.
You'll find the Analyze Results tool when you're looking at any result set in Web of Science, including the Marked List.
When you run Analyze Results, you can choose to show the top 10, 25, 50, etc. funding agencies for your result set.
This video goes over funding data coverage in Web of Science Core Collection.
Search the Web of Science like a master.