To find the information you are looking for, I suggest checking:
* Hasbro's official website or financial reports: Hasbro is the company that owns the Monopoly brand. You might find sales figures in their annual reports or press releases.
* Market research firms: Companies like Nielsen or NPD Group track consumer spending and might have data on Monopoly sales.
* Retailer websites or reports: Large retailers like Amazon or Target might publish information on their top-selling games.
Remember that these numbers may vary depending on the source and how they define "Monopoly games."