I'm surprised a high end panflute library hasn't really been made yet. I've mainly only been able to find a few low end libraries with only a couple of articulations like staccato and vibrato.
There was one I found that seemed like it could be good - The Essence of Panflute. That one has more articulations than most (Long Notes, Crescendo, Vibrato, Wild Vibrato, Frullato, Portamento, Staccato), however, I heard that it isn't multi-velocity
There was once a free one made by ThomasJ. I know you wanted a pro one, but this had a fair few articulations, and the results Thomas got with it were great (although I think he only put part of it online, because this was the day of dial-up internet). If you can find it, it's in Giga format, but imports well into Kontakt.
Where can I buy or download the ThomasJ Panflute?
Well I found the original thread here on the forum, and the link to the file is long gone.
I don't think I kept the original Giga file, but I have the Kontakt file I got by importing it. I can't imagine Thomas_J would have an issue with me sending it to you, given that it was free to everyone. PM me if you want.