I am finally able to get this to work. Changed the --proto_path to point to the root of all proto folder hierarchy. I got it working in the morning. Just now saw your solution. I will accept it - you are right. I thought it would be some such silly mistake in paths. Yesterday I was lost in VS Code, Visual Studio and PyCharm.

C:\tmp\proto>python -m grpc_tools.protoc --proto_path=c:/tmp/proto/ --python_out=c:/tmp/generated_python_files --grpc_python_out=c:/tmp/generated_python_files c:/tmp/proto/common/*.proto

I also changed to grpc_tools.protoc to generate the client and server stubs. And now *.proto also works. Able to generate for all my files (one folder at a time).

Thanks