Start with instinct, then search
Start with your gut feel. You built this product because you observed a problem somewhere. Who did you observe it at? What role were they in? That instinct is your starting point.
A network-heavy interview pool is a biased one. People who know you will moderate their feedback in your favor. Aim for at least 6 out of 10 interviews from outside your direct network. If you cannot reach that ratio, your network may not yet cover your target market, which is itself a useful signal about your go-to-market (GTM) reach.
Three sources, in priority order
If you have existing customers, start with source 1. If you are pre-revenue or have fewer than three customers, start with sources 2 and 3 and return to source 1 as your customer base grows.
Interview the champion and the decision-maker separately. Do the champion first, they are more accessible and their account of the day-to-day frustration gives you context for the decision-maker conversation. The champion gives you Push and Habit zones. The decision-maker gives you Anxiety and Pull zones.
If you interview them together they will moderate each other, you get a curated version of the purchase rather than the real one. Do not be surprised if their accounts diverge, a champion who describes urgency the decision-maker does not mention tells you the pain was real but not yet visible at leadership level. A decision-maker who emphasizes risk factors the champion never mentioned tells you where anxiety lives.
Competitors publish case studies and testimonials on their website and on review platforms like G2 and Capterra. These are people who have publicly confirmed they switched to a solution in your space. Reach out on LinkedIn with the same low-pressure research framing you use for any outreach.
Search LinkedIn, Substack, and relevant community forums for people who have written about the problem your product addresses. If they fit your target profile, reach out directly and reference specifically what they wrote, not just that you saw it, but what in it was relevant to your research.
Three causes, in order of likelihood
If after four to six weeks you have fewer than five interviews completed, that is a signal worth examining, not a scheduling problem to push through.
In all three cases, the inability to book interviews is a data point. A GTM motion that cannot reach its target persona in the research phase will face the same challenge at scale. If none of the three adjustments produce results within two weeks, consider whether your ICP hypothesis needs to shift before your sourcing approach does.