Don't own a pair of the speakers, but have you tried McIntosh parts for the tweeters? They have a surprisingly large inventory of parts to support older gear. If they do not have the exact tweeter, you might ask if they have a recommendation on a replacement tweeter. That failing, ask the couple of speaker repair vendors who adverstise here on AK what they might recommend. They may have a cross-reference. Will need to match the impedance and sensitivity to get proper balance out of the speaker, unless it has an L-pad in the circuit.
Accuphase T-106 V Bryston BP-25 & ST-3B Cary SLI 80/PH 302/CAD 572SE MkII Joseph Audio Cinergy 5.1 (x2) McIntosh MC50(x2)/MVP861/MR65A Micro Seiki DDX-1000 SME309/Jelco SA-750DB/Kp-b/AT150Ti/V15VxMR/DL-303/2M Black Sony TA-F707ES/SS-M3/ST-J75 Yamaha T-85