I have lots of vintage drivers. If you are careful, you don't need replacement. I also have a few current drivers, but they are a bit boring. ;-)
Those slot tweeters are just heckmotors. Invented when JBL "needed" something above their "large" horns. A proper horn will work for 3 oktaves, so a proper treble horn should handle 2,5-20 kHz. And a proper midrange horn should handle 300 Hz - 2,5 kHz