A domestic commericial supplier is J.L. Hudson, Seedsman, in California.
The seed is listed and described as "bee food" in the 1996 catalog (J.L.
Hudson sells a very large variety of seeds for uncommon, open-pollinated
plants from around the world.)
The address: J.L. Hudson, Star Route 2, Box 337, La Honda, California 94020
(Another address, for requesting a catalog ($1): J.L. Hudson, P.O. Box 1058,
Redwood City, CA 94064)
The supplier does not list a phone number, and does not take phone orders,
so I'll mention the seed prices from the catalog: $1.25/packet, $5/ounce
(also fairly expensive!)