This is a flora with a long and troubled publishing history!
The original edition (1893-1900, Trimen and Hooker) has of course been unavailable for many years, although still immensely valuable to systematic botanists. In the 1980s, the Smithsonian Institution Press (which has now ceased publishing altogether) issued revised editions of volumes 1-9. With a further 7 volumes to go, publishing was then transferred to AA Balkema, in the Netherlands. They published volumes 10-14 (including a revised index to volumes 1-14).
Balkema then became part of the Taylor & Francis publishing group (2003/2004) and volume 15 covering ferns was published by Science Publishers in 2006. To the best of our knowledge, plans for volumes 16-18 have been abandoned.