At the bottom of https://doc.nuxeo.com/nxdoc/910/nuxeo-stream/ , https://doc.nuxeo.com/nxdoc/1010/nuxeo-stream/ (but OK in FT), the link nuxeo-importer-stream README directs to https://github.com/nuxeo/nuxeo-platform-importer/tree/master/nuxeo-importer-stream , which itself redirects to https://github.com/nuxeo-archives/nuxeo-platform-importer/tree/master/nuxeo-importer-stream
The correct links seems to be since NXP-25092 (repository merged into nuxeo/nuxeo)
https://github.com/nuxeo/nuxeo/blob/master/addons/nuxeo-platform-importer/nuxeo-importer-stream/README.md