You should be able to buy it locally, Kava kava is a fairly well established product. If not, through Amazon.
As for ayurvedic, I googled "ayurvedic urination" here are some hits:
At the bottom of this page there is a list:
http://www.allayurveda.com/ail_urinary.asp
Another one:
http://www.slideshare.net/drsaurabhjpr/ayurvedic-therapy-for-urinary-system-disorders
They both mentions herbs I never heard of before.... (punarnava, shatavari,etc)