First and foremost the best network is word of mouth. It’s definitely hard, especially in the UK where I’m based, to find a passionate and skilled career Barista to hire. But you can’t go wrong with hiring people you’ve heard great things about, trust and want to work with. The best network is the one you build around yourself based on previous experiences and gained knowledge.
Coffejobsboard is the go to for many and it’s a great site. I recommend it. However you must be clear about what you’re offering and what you expect in return.
Email roasteries (who have access to a vast amount of people both internally and externally via wholesale accounts). If it’s truly a unique offer then I’m sure roasteries would be willing to ask around amongst themselves and aid in spreading the word if you’re very very polite
Join groups on Facebook and post jobs there (if the group allows it). There are plenty of Barista focused groups there with a constant stream of potential.
If you’re somewhat rural or in a small town hire locally. Hire whoever has the biggest desire to learn and become their mentor. Building someone from the ground up is a good option but be prepared to invest time, effort and money into this person. There’s forever risk involved but what’s life (and being a business owner) without a little risk?
Other than the above I’m not sure what else can be done.
Hope I’ve been of some help