Only thing I can really think of that may work off the shelf would be ribbons or planar tweeters. If you look at
partsexpress for Aurum Cantus ribbons, most of them have "rated" frequency response out to 40khz....if that's a -3db point for them, then another half octave up to 60khz may not be that bad response wise. Maybe look into LCY's aswell, such as the LCY130.
Electrostats too
maybe...but a decent pair would be ungodly expensive.
But this is by far one of the oddest requests I've seen on this forum yet. And, considering the member base, that's quite a statement //content.invisioncic.com/y282845/emoticons/tongue.gif.6130eb82179565f6db8d26d6001dcd24.gif