Well, as there are neither "members" or a "list", as such, you just never know who might drop by.

Lack of dark skies on their home continent drove the European telescope consortia to South America decades ago (a quick lookup tells me the first ESO site in Chile dates to 1969). It was only a matter of time before the same situation confronted US researchers.

Since the other posts on this thread seemed to be concentrating on red tape obstacles to the construction of observatories, I merely wanted to remind them that practical considerations eliminate most theoretically ideal sites long before reaching the permitting stage.

As the owners of portable scopes among us well know, the darker the sky, the harder it is to get to... then think about getting all the materials and contractors there to build a state-of-the-art facility, and the power and communications cabling to run it.