We built up a partner network worldwide, so we had to find relevant partners who would help serve our potential customers in the relevant way that already had those customers. They are easyish to find and approach because they are trying to achieve a similar goal, although sometimes more generically if they are integrators (selling software, hardware and services). Sometimes they sell a competitive product so our USP had to be tight - such as not requiring a year of services to start up but maybe an hour or two.
Others were complimentary tech partners and very kindly helped spread the word, and got a foot in the door for direct engagement.
If each partner has 10 good customers, then thats 10 partners you have to engage with. We were more often than not involved with the relationship with the customer, and got direct knowledge of the customer problem, how well we fit solving the problem, identify UX issues, sales issues, support issues etc..
It’s been a successful way to start.