A number of existing resources can help you find out how much money is being spent on specific market segments in many different countries. They may not address your specific product or service, but they can tell you a lot about that group or market segment of similar things that people are spending money on in specific countries, what percentage of GDP that represents, and so forth.
This list includes Export.gov, US Census, United Nation Internatíonal Trade Association, etc.
Some are free or have a free version:
There are some with paid subscriptions but others like US Census only require registration:
https://usatrade.census.gov/index.php
General information sites include
And of course you can always get help at your local Small Business Development Center (SBDC) or contact us.