Some things, in theory, sound good, but in practice... not so much...
ISO's sole purpose is to archive and emulate a DVD or BRD and by using said file format we can use it to write a real DVD/BRD or a USB thumb drive and be able to boot the PC. Windows and other OSes need that function as well as live CDs but office... not so much. You can't really boot straight to MS office.
As such, there is no real need (or at least I can't see one) for an ISO specifically, and all you have to do is download the versions of the office you like/want from here, and write them directly on a thumb drive, each version on a different folder. It's the same thing but with fewer steps and less hassle and also the convenience of combining things like you can have a thumb drive with windows AND office (and other software). If for some reason you want everything in one file, use WinRAR or 7zip I guess. Keep in mind if you have the files in separate folders and not an ISO, its easier to update with newer versions too.
That is probably the reason you haven't seen a pure ISO office so far.
Unless the OP can describe a real need soon, I think it will be wise to close this thread.