TL;DR - Make each data source a package instead of a module.

Changing data_sources folder to contain foldersinstead of a file for each source.

It will make the code less "monolithic" without creating a meess, you could implement your own clients/wrappers for those clients which will make the code much more easy to maintain. add files for testing, etc etc.

Have a look at CloudQuery's solution. (although it's an extremely different product for a different use case..)
I guess it's better to do that sooner than later ;/