The website Kivalin (based in Queensland) says they have been selling online since 2001, although I've just discovered it. It pays to keep your eyes and ears open! Their sizes go from 16 through to 24-26 (3XL)
Visit their website and see what you think. The clothes are "designed in Australia" and go up to 24-26 (Size 3XL).
(Editor's note: While this website claims to be Australian, the feel and look of the site itself seems to be an American one. I only say this because I've found so many on-line stores claiming to be Australian but not so. If any readers find this to be so with sites they visit, then please let's know so we can share this information.)