Thasp,

Have you tried any DIY audio forums? They may know which tweeter to buy as a replacement. You may need to replace both to get the same sound.

The Vifa XT25 is an excellent tweeter. How did you come across it?

Is this your post?
http://www.diyaudio.com/forums/showthread.php?s=d7c33fcc22579546b81acc09847bfe3d&threadid=142119

You can also contact Madisound and ask for advice. If you are going to replace 1 tweeter, I would strongly recommend replacing both.

http://www.madisound.com/services/retrofits.php

You can also read up about well-rated tweeters on Zaph's site here:

http://www.zaphaudio.com/tweetermishmash/