It doesn't look like many companies make Beryllium tweeters. I could find only Scanspeak (a company that Meridian have used before).
Scanspeak Beryllium tweeters go for around �600-700 /pair. I think this would result in a substantial increase in the cost of the new speakers or any upgrades.

Tim

RoPieee Allo DigiOne Signature, 561, DSP5000, DSP33, SW1600, M3.
HH1 Number 48