In alphabetical order:

Centre for the Understanding of Sustainable Prosperity

https://www.cusp.ac.uk/

Green Economy Coalition

https://www.greeneconomycoalition.org/

Institute for New Economic Thinking

https://www.ineteconomics.org/

International Society for Ecological Economics

www.isecoeco.org 

London Mathematical Laboratory

www.lml.org

New Economics Foundation

https://neweconomics.org/

OECD New Approaches to Economic Challenges

http://www.oecd.org/naec/

Promoting Economic Pluralism

https://economicpluralism.org/

Rebuilding Macroeconomics Network Plus

https://www.rebuildingmacroeconomics.ac.uk/

Reteaching Economics

http://reteacheconomics.org/

Rethinking Economics

https://rethinkeconomics.org

UCL Institute for Innovation and Public Purpose

https://www.ucl.ac.uk/bartlett/public-purpose/