Eureka! Having searched high and low over the internet for this most elusive, but essential, herbal constituent of absinthe, I found it this past Saturday, being sold in quart-size plastic containers for only $4.95 per plant (in the artemisia section, along with various other ornamental mugworts) at one of the best local garden shops, Berkeley Horticultural Nursery, on McGee Street in Berkeley (right around the corner from Monterey Market). I'm not sure whether they do mail orders, but it's a great opportunity for the DIY crowd here in Northern California.