There are many more archives in the world than there are digital archives. Digitizing materials takes a long time and certain materials are prioritized over others. That being said, digital archives also tend to be a part of traditional memory institutions — universities, museums, archives, historical societies, etc.
Google is an amazing search tool, but often it can be more difficult to find obscure resources. That being said, it can definitely help in your search for Digital Archives. Below are some strategies that can help: