Check the continuity of the removed tweeter with a VOM meter (I use an original Heatkit MM-1 available on eBay for $20) and do the 1.5 volt battery click & scratch test mentioned above.
Celestion A3 tweeters (also used in the A1 and A2 speakers) or the replacement diaphragms are no longer available from Celestion. A1 speakers show up regularly on the United Kingdom eBay website for $300 or less and are small enough to economically ship to the USA. You would also end up with a midrange spare speaker (assuming it is the same as in the A3 cabinets)
The part number for the A series 3 bar tweeter is T4969/P. The 3 bars refers to the 3 bars in the casting to protect the dome. I got this number from the box of my spare tweeter I have the earlier 1 bar castings in my A3's.
Go to www.ersatzteil-versand.at
do an "artikelsuche" (article search) for the number T4969/P and something extremeley similar shows up except that they list the manufacturer as Onkyo. The part number and description are so similar to what is printed on my spare tweeter box it would be worth 81 euros to see what shows up.
I have designed an adapter plate for either a Scan-Speak Revelator Tweeter D2904/710002 4 ohm, 1" soft dome, 70 mm diameter magnet, $220 or a Vifa D27TG35-06 6 ohms, 72 mm diameter magnet, 91 db, $37.50..Both are available from:
in Burbank, CA
I only modeled the front flange of the tweeter to save time. I have not built any of these yet but the price would probably be $400 for a pair of adapter plates and speaker flange modifications. But when you are done you would have replaceable tweeter for a long time to come. The 2 protective bars are drawer handles available for $3 each.
Other possibilities are:
voice coil rewinding in the uk
voice coil rewinding in australia
in Florida can rebuild the woofer and replace the midrange but no longer have the 4 ohm diaphragm for the tweeter.
If you want the drawings (and 3D geometry file necessary for the machinist to make the curved edges) for the adapter plate and tweeter flange modification contact me at email@example.com