OK, as it always happens, I found a github repository of wxPython 3.0 15 minutes after the question here (https://github.com/wxWidgets/wxPython). Here's my experience if someone is interested.
Unfortunately, I got ahead of myself and installed wxWidgets from source without wxPython. It seems that build script in this repository can build and install wxWidgets and wxPython at the same time. Luckily this script has option that allows to build wxPython only, so the build command was
python build-wxpython.py --install --no_wxbuild. After the installation I tried
import wx in python terminal to test it out, but got an
missing _core_ error, which was fixed by reboot.
However, despite of working hello_world example kicad building script tries to find
wxversion module and fails. But that's another question.