Type stubs are sometimes packaged directly with the library. Otherwise there can be some external libraries to provide them.
Numpy
Starting with numpy 1.20 type stubs will be included in numpy. See this changelog and this PR adding them
Before that they could added with the library https://github.com/numpy/numpy-stubs
Pandas and Matplotlib
There is no official support for these libraries stubs but you can find unofficial stubs in this project: https://pypi.org/project/data-science-types/
You can either install this library as a dependency or copy only the relevant part in the type stubs folder of your project.