Ribbons that can be crossed over at 1.5K will be expensive. Have you considered the Fountek NeoCD2? It can be crossed at 2khz? Its limited vertical dispersion will make this a speaker that requires the listener to be seated, but you could later add additional ribbons to make a full tweeter array. Both Jim Griffin and Rick Craig have used this single ribbon tweeter configuration in a midwoofer array using either the 5" Fountek or Aurum Cantus, and both were well recieved by listeners who heard them.

Regardless of which tweeters you use the crossover is critical for achieving their full potential. When I'm building a cheap line array I don't hesitate to "wing it" with my inadequate crossover design software, but if I were spending significant $$$ I would pay a bit more and have one of the line array gurus design a crossover that optimizes the sound.