Early phases, go direct (meet in person), after that, go to their professional associations (it’s slow but you’d get a bit more credibility along the way). Most are on Linkedin these days, so, marketing there will get you the digital social butterflies.
Once you have revenues and can afford a sales team -
https://www.amazon.com/Predictable-Revenue-Business-Practices-Salesforce-com/dp/0984380213
DM me for more, as I’m currently building a sales team pipeline with around 20k prospects