The reference page I use is Index of ./jira-software/REST which gives access to lots of versions of the Jira Software API but stops at 7.3.1.
I guess this might mean that there are no updates to it since then and it is a stable API?
Hope this helps although it is not for the version you were looking for but should point you (and others in the future) where to look for the published API pages.
Been wondering the same thing myself for some time. I mean, the source is available through my.atlassian.com, but sometimes I want to link someone to a particular class without their having to download the source.