I teach #leanStartup. I practice what I teach. I push entrepreneurs to be bold and try to hold myself accountable to the same standards on my own startups and ideas. I love helping entrepreneurs design and run experiments. @neighborrow taught me that there is a difference between a product that customers should use vs one they would use. @photogether_ showed me how to get from idea to revenue in a day. I travel the world teaching classes, mentoring, running workshops, etc.
The best way to get in touch with them to do problem interviews is to think like a borrower. On the one hand you want to avoid being sneaky, but on the other hand you are truly trying to solve a problem for them and not trying to spam them right. So the final judgement is yours, but I think it is fine if you approach them in your natural habitat. Do not book an appointment and take a spot from someone else or make them think they have a spot coming up to help someone, but go to their office. You will know after 5-10 of them if they have the problem you think they have to the degree that you think they have it. Here's the thing though, and I feel like a jerk saying it but would feel worse not saying it. If you are asking on quora where to reach them, it means you have not reached any yet. Which means you haven't talked to any yet. If you are looking to get opinions on mockups it means you have a solution already. Which means you are not really doing customer development but doing pre-product usability. That is better than doing post development usability but worse (in my opinion) than doing pre product customer development to truly understand the customer/problem. When those two variables are more known, it is shocking how much easier it is to get the product part right.