Well, Wavecor makes a few good ones... You might check with Gowa to see if he has any Rival drivers available for you as well. For great bang for the buck, look at Peerless 830883.
It's a versatile tweeter so you're not really limited in options. Is there a few drivers you have specifically in mind?
Box size and driver size? That tweeter can cross really low so 7-8 is possible, but a 5" or 6" is also good. The 6" CAC SB ceramic driver is on sale now, can do a small box or large one.
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