You can see a list of jupyterlab extensions by browsing the jupyterlab-extension topic on github (as suggested by the jupyterlab docs): https://github.com/topics/jupyterlab-extension
Silly me. The answer was in the docs all along. In order to publish you need to be logged in from your NPM cli. So either do npm login if you already have a user on npmjs.com, or npm adduser to create one. I would, however, appreciate a more informative error message.
https://skimdb.npmjs.com/registry/_all_docs This is a current method to pull all the package names. The URL search is http://registry.npmjs.com/-/v1/search?text=<searchstring>&size=20 Edit1: 3 years later (Mar 2021) and this endpoint still works. Glad it’s still being helpful to folks 🙂 Edit2: Still working in April of 2022 Edit3: Still working as of February 2023