Phil
As usual I'm lating in reading, and therefore replying, but double
flowered Sarras are (reputedly) available for purchase if you've got
the bottomless pocket to afford them. Best picture of one (for sale)
that I've seen is in the Hinodo-Kadan nursery. Forgive me if I've
mis-spelt nursery name - it's the one in Japan (and it's VERY
expensive, as is the postange because the nursery is on a tiny island
that's almost in Hawaii and everything - including post - is expensive
in Japan - so you pay a heavy price for their having to ship it via the
mainland first.)
Regards
Paul