David!
You're right about french tarragon not being seed-grown. I think tarragon is similar to rosemary and lavender, with the plants branching out from a central stem -- not something that's easy to separate, although you could try cuttings. I could be wrong about how tarragon grows.
I wonder if it's fallen out of fashion or something... I didn't see any at Black Creek when we were there this spring, and they have darn near everything.
Check out the spring swap thread at the top of the forum! We're getting together this coming Saturday at Terri's beautiful place near Lucketts, VA.