We need to split your question into two parts...
"Hard-to-find customers" is a red flag to me. That sounds as if you have a product or service looking for a market, which is pretty tough way to build a business. Unless you have figured out your product-market fit (which assumes you know who your market(s) is/are) you should not be selling yet.
If you have confirmed that there is a market need and your product/service is of value, then you should be selling. There are a variety of strategies to get to "hard-to-reach customers". Often there are existing channels that already own relationships with your targets, and partnering can be a way to get to them quickly. Sometimes an audacious, disruptive business model can help gain the attention of your targets. Creating industry notoriety through luminary customers or media exposure can also help you get noticed by targets, but that will require a purposeful, focused marketing effort. And if you have already built relationships with some customers, you should be able to ask them for referrals to other prospects (assuming they are happy with your solution), and seek their advice on how best to approach targets.