Is there a list of the largest academic journal publishers, ordered by the number of journals they publish?
There are a large number of predatory publishers who publish 300+ journals of no real value. So there is no way to include all publishers.
However, if you would be satisfied with scopus indexed journals, then you can download the excel file, sort it based on publisher and filter it. Thus, you will get a list of publishers with the number of journals. Of course, the list will be confined to scopus indexed journals (around 40000 journals by 4000 publishers).