Expedia and Travelocity couldn’t route my wife from Anchorage to Ushuaia (Tiera del Fuego) to board her trip to Antartica. My sense is that their algorithms just don’t support 5- and 6-leg journeys, much less 10- to 12-leg round trips.
The Wikipedia article on most cities / airports lists which airlines fly there and then I work backwards from there.
There are definitely connections out of Copenhagen and I think I remember some fights from Iceland which is easy to reach on Iceland Air (although WOW Airlines shut down a week ago).