I don't think there is another Ushuaia.
Pretty enterprising people down there on both sides of the Beagle but I can't point you in the direction of anyone in particular.
Push comes to shove and if it is major they could fly someone down from Puerto Montt to Puerto Williams. I've known of that happening before.
Are they part of the group of 5
boats on their way down from FP towards the Horn at the moment?
PS - tell them not to think of going directly through Chilean waters to Ushuaia - that will end in serious tears.