Some publishers have made it easy to get an overview of currently existing paradigms in economics, including non-neoclassical paradigms:
- Modern Cambridge Economics: Each book is by an expert on the selected topic. (Previous mention here.)
- Schools of Thought in Economics: From Edward Elgar, each book is edited by an expert and consists of reprints of important papers from that school.
- International Library of Critical Writings in Economics: From Edward Elgar as well, each book is also an edited collection. Many of these are more on a field than on a school, but I like number 21, on the Post Keynesian theory of growth and distribution.
- M. E. Sharpe: I do not have a book series for this important publisher of heterodox economics, including the journal Challenge.
The books in the Edward Elgar series are probably too expensive for most individual purchases. Perhaps you can request some of interest from an academic library. Some of these books are more than a decade old, with articles in the collections going back even more decades. But, by looking at authors and journals, you can can get a hint of where to look for more contemporary work in a school of interest.
Compare and contrast Paul Krugman on this topic.