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 Cary SLI 80, SLP 03, PH 302, CAD 572SE MkII Dual 701 Ortofon K-b & 2M Black, AT33R & AT150Ti, DL-303 Joseph Audio Cinergy 5.1 (x2) McIntosh MC50(x2), MVP861, MR65A Sony TA-F707ES, ST-J75 Yamaha T-85, TX-1000