Several ways come to mind.
Formulate your idea into one (or better all) of the following + you'll know by interest level if you have a winner.
1) My favorite. Start a Meetup Group (set the zipcode of group) to match the zipcode of a US city where most people originate travel to your target destination.
For example, If your targeting running tours in Chang Mai Thailand, research what city people in US most travel from to visit Chang Mai.
Then run Meetup events related to Thai Travel topics.
2) Package information about Thai Travel into a PDF + sell it via Facebook Ads.
3) Start a Kickstarter project.
4) Speak at existing Travel Meetups + other groups + related conferences about your idea.