I logged onto our Volume licensing site with Microsoft and typed Office Online.  Zero results. Hmmm. Maybe I typed it wrong. I’ll look under the Office category. Nothing. How about the Servers category? Nothing. OK I’m stumped.

Luckily Google and Max Fritz (ironically from Microsoft) solved my dilemma.

http://nowmicro.com/blog/where-to-download-office-online-server-2016

Office Online Server is under your Office package.

So under Office Professional 2016, click download, 32/64 and click download again. Then the site will display all of the download files available. One of the files is the Office Online Server iso.