I've been searching for a library I can import and superimpose on my wxpython-based layout to give it a Flat-UI look. Does there exist libraries that can be used along with wxpython or just python?
You can use the custom widgets in wx.lib for the flat look, however there is no way to apply a "theme" to all the widgets in wxPython. Why? Because wxPython tries to wrap the native widgets on each platform, so it does its best to look native. If the native widgets are flat, then you'll see wxPython doing that too. Otherwise, you have to use the custom widgets.
If you want your app to have the "flat" look on all platforms, then you'll probably want to take a look at some other toolkit that allows theming, like Kivy or Tkinter. I think PySide/PyQt might even allow a little theming too.