Why are they rare? I was able to source a 'Haru no Sono' (sport of Issho no Haru) as a nursery plant from France (had to search hard). It is really one of the best large-flowering azaleas, if you asked me. And I talked with some other people, and they also rate it highly. A US azalea hybridizer told me he had sown tens of thousands of seeds from his 'Haru no Sono', but none of the seedlings he got to flower were as good as 'Haru no Sono' itself. The thick petals, range of different flowers, and very dark glossy foliage are hard to beat. Puts out tons of flowers as well.
It seems you actually have an all-purple sport. Which is arguably nicer as a landscaping scrub. Maybe the other one has the light pinks?
Luckily somehow mine has a nice range (but not quite perfect) range of flowers, which is uncommon in the nursery trade.
Mine is just starting. I love it when the yellow blotch turns purple.
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Oh, and if you missed it, we were talking about where in the US to buy rare satsuki:
A friend & I bought 5 and 6 from Nuncios (page 35) last year, all at $8 each and they were all sizeable, much larger than we were expecting, all lived through winter here just fine. I highly recommend them.
www.bonsainut.com