How to import module inside sub-package of a package in python without knowing the sub-package name

Question

I have my python directory structure something like the following:

Directory Layout

data
 |
 +-- __init__.py (Empty)
 |
 |
 +-- foo.py
 |    |
 |    +-- __init__.py (Empty)
 |    |
 |    +-- a.py
 |    |
 |    +-- b.py
 |
 |
 +-- bar.py
      |
      +-- __init__.py (Empty)
      |
      +-- c.py
      |
      +-- d.py

To import modules

a, b, c & d

I am trying to use importlib.import_module to import these modules. e.g.

mod_a = importlib.import_module("data.foo.a")
mod_b = importlib.import_module("data.foo.b")
mod_c = importlib.import_module("data.bar.c")
mod_d = importlib.import_module("data.bar.d")

Is there a way by which I can import the a, b, c or d module directly without knowing the name of sub-package in which they are present?

(Maybe modifying any of the __init__.py files ??)

That is, I want to do something like this:

mod_a = importlib.import_module("data.a")
mod_b = importlib.import_module("data.b")
mod_c = importlib.import_module("data.c")
mod_d = importlib.import_module("data.d")

P.S.: The names a,b,c & d are unique