These models were published, each in two or three parts, throughout five years. I consulted some databases, so that you know what you are searching for:
(volume/issue)
Colossus of Rhodos 38/7 (1994)
Pyramids and Sphinx 38/20 (1994)
Lighthouse on Pharos 39/6, 39/7 (1995)
Mausoleum in Halikarnassos 39/14, 39/15 (1995)
Hanging Gardens of Semiramis 40/8, 40/9, 40/10 (1996) (these were also published by GPM)
Temple and statue of Zeus in Olympia 40/23, 40/24, 41/1 (1997-8 )
Temple of Artemis in Ephesos 42/14 and 42/15 (1999)
So, basically, these are nearly 20 years old models. They can be bought from collectors at exhibitions here, I think they are not THAT rare, but it can be a problem if you live overseas. I think I remember US site selling ABC magazines, but I am not sure it still works...
GPM maybe published more models from this series, I am not sure whether they did not publish the Olympia, too...