I developed a unique software that solves a particular problem. There is interest in the product and sales are ok. But when I approached (at least 10) gurus who speak or write about that topic, offering an affiliate link or just for their opinion. Not one responded. So i am thinking that my email must be wrong or there must be is a specific way to approach them.
Identify what these "gurus" need for their work or how you can contribute to their success success. If you find a way on how to contribute, provide them with free value and the offer to get back to you in case it was helpful (or they need more information or insights etc).
If they get back to you, develop a potential affiliate engagement from there, again, pointing out the benefits on her or his side.
Even if they don't end up engaging with your product, they will remember your name (due to the value you provided - if you really did) and your expertise as soon as a similar topic comes up.
Hope that helps :)