Hi
These would be the common methods:
1. Contact them directly - but make sure you offer something in your email that makes it worth their while to answer your questions.
2. Run a paid/free survey (lots of platforms offer this service - just focus on your target market). If it's a free survey, offer a prize (and give it) to one of the participants.
3. Try using Google Alerts for variations of the phrase "company retreat"
Obviously you would need to know what you are doing with each of the above options so that your results are accurate. The wording in each question is important.
I've successfully helped over 300 entrepreneurs and I'd be happy to help you as well.
Good luck