By researching avant garde art movements of the 20th Century, I came across some amazing resources that I would like to share:
Tate’s online resources are vast, from dada to colour theory, you just need to rummage a bit. They provide detailed information with lectures, papers, theories and research.
Another resource is Graphic Design History:
This site gives condensed insight into select topics that are sometimes overlooked such as avant garde typography. It is very useful if you are looking for specific information.
If you are into Dada, the University of Iowa has a Dada archive with lots of information including complete periodicals, books and leaflets available to download.