They do seem to exist; this site has Volumes 3-5 for sale:
http://www.angusrobertson.com.au/sea...diatype/EBook/
And Amazon seems to offer Volume 6, but I can't imagine that a Mobi --> Epub conversion will work well for a comic book.
I also read an online article that seemed to indicate that Amazon and the iBooks store used to carry all 6 volumes, but the quality was apparently fairly bad and the books were pulled - presumably for cleaning up.
If anyone knows a site where all 6 can still be purchased as pdf/epub, then I'd give it a try.
EDIT: And then there's this, which appears to be an Australia site. Not sure if I can order from here as an American.
http://www.ebookbop.com.au/book-sear...earchBy=author