Have you read the Docker FAQ?
Links to Community Applications are all over the place. In the getting started of the Docker FAQ, Limetech's Official 6.2 Manual, my signature, the All Applications Repositories and Support Threads, along with the thread being stickied itself in the Plugins section.
As to the link to the repository, I well understand lsio's reasoning behind not publishing it (and they are not alone) -> it simply makes support easier as then its not their problem getting unRaid to populate the dropdown lists. They would rather (rightfully so IMO) pass everything off to CA and let me deal with the back-end stuff. An analogy would be an app for your Android device telling you to manually install the .apk instead of going to Google Play
But, either way, manually adding in repositories is still supported on the current version of unRaid, and I also maintain a stickied thread that has all of the containers within the particular repositories with the repo's link, support threads, etc. All Application Repositories and Support Threads