There's a guy at DiyAudio who has completed one group by of Airborne AMT tweeters, and is preparing to do another one.
Prices are pretty excellent. Probably take a few months for delivery from CN.
Details are here:http://www.diyaudio.com/forums/planars-and-exotics/312560-looking-hygeia-airborne-amt-tweeters-designs.html
Don, Donno, or "Hey you" all work for me, But never "Mr Johnson"