The there,
No worries about the link. Please note that the accessibility plugin is made by excellent PayPal team, not amCharts team and therefore is not maintained or supported by amCharts team.
That being said, it should be fairly easily to incorporate it into your WP install:
1) Download the plugin from their github page:
https://github.com/paypal/amcharts-accessibility-plugin/blob/master/plugins/amstock-accessibility.js
2) Put it somewhere on your web server.
3) Add it at the end of the Resources block when creating a chart.
A few things to note.
I haven’t used or even tested the plugin myself. It looks like it is geared towards Stock Chart product and might not work properly with other chart types.
Also, it was created using quite old version of the charting library as a base. It might also not work with the most recent one.
I suggest trying it out. If there are specific issues, or it does not work, you can take it up with the authors. I believe they have their contact details up on the GitHub page.
I hope this works for you.