I just placed another order for fresh wasabi, and thought I would post the information for you. I normally buy a single rhizome at the Japanese market (at $99 a pound). But for a party, I order in bulk. It is light years better than the paste.
To add to the delight, I found a shark skin wasabi grater at Sur La Table (why they stock so esoteric an item is beyond me). This small ritual of grating fresh wasabi helps dazzle guests and distract them from the odd shapes that even my most studied efforts produce.
I believe this is the only source for fresh wasabi in the US. It is quite remarkable. Single rhizomes BTW make very nice presents to fellow sushi lovers, who present them in turn to their sushi chefs and glide just a notch higher on the "what a nice customer, what special dish shall I make to impress them tonight" scale. Best, AZ