Google Calendar is awesome and I haven't had any accessibility problems with it. I had to use it for a job and loved it so much I use it exclusively now.

In what was does it not work right? What aspect of it are you looking for that they seem to be lacking?

Have you tried the IOS calender, the Google calender, or the Outlook calender? These have been quite accessible.

I juggle a good handful of calendars (work, family, etc) in iOS and in Outlook on Windows. Most things I need to track are exportable, or subscribable to with these tools.
Do you have a different use-case/platform setup? Does "online" necessitate a browser-based solution? Most calendar "views" are very table-oriented by nature, not always the easiest from a screen-reading perspective.

I just use the Calendar apps on MacOS and iOS which are accessible, integrate with online calendars from several providers, and provide notifications about upcoming events.