We're not allowed to provide sources, but I can tell you to look for True Kava Labs noble kava certification. They independently test kavas from different vendors and will certify that a vendor only sells noble cultivars.
Here's a link to their site. They have some great info about the herb.
http://www.truekava.com
As for your attitude towards benzos, I personally wouldn't be against them if they're helping and you use them responsibly. Kava lacks the risk for physical dependence, and phenibut is less likely to cause physical dependence with 1-2x/week usage, so I think they're much better than benzos if they work for your. However, I wouldn't completely discount benzos if youre unable to find an alternative.