What info are you after? From your very brief post it sounds as if you want info on where you can buy a working unit.
Only TWO companies make and sell plasma tweeters - Acapella and Lansche. Both are German. Acapella used to sell the plasma tweeters individually but I think they now only sell them as part of their speakers. Lansche is the same, but they closed the door on tweeter sales many years ago. Unless I am very much mistaken, you will not be able to buy these from the factory.
I think that Brian Ackerman from AAudio Imports is a member of Audiogon, so he may be able to advise you on whether you could buy one.
Your other route is to DIY a pair. I have seen circuit diagrams on the web. My own skills are very modest - I can't even put together a doorbell kit from Radio Shack let alone tackle a project like this!!
Going on specs alone the Lansche is more desirable. The plasma flame is twice the size of the Acapella, consequently it can go lower - 5kHz for the Acapella, 2.5kHz for the Lansche. Neither unit tolerates low frequencies beyond the stated crossover point very well, so steep filters are necessary. The Acapella has a crossover built in - the point and slope are configurable by changing internal components. Not sure about the Lansche.
If you want to know what they sound like - I have a pair of Acapella Violons.