An update, after I have been working on accessibility topics in the last weeks.
Basically widget.SetAccessible should work. If it does not work, try a 32 bit build. The 64 bit builds do not always work.
The usual pattern in wxWidgets, though, is to create a wxAccessibility instance only on demand, by overriding the widgets’s method CreateAccessibility. Currently this is not available in wxPython, but I have submitted PRs for wxWidgets and wxPython. So, if testing is successful, this functionality should be available in the next wxPython version. At that time I will also post example code here.
I have also started work on accessibility support for wxGrid. The first step is to implement this in wxWidgets and then at some time it should arrive in wxPython as well.
(Most widgets inherit accessibility support from the native Windows widgets, but wxGrid is a generic widget on Windows and therefore all support needs to be implemented ‘manually’.)