This article is based on material authored by members of the news.newusers.questions Moderation Board and nnq-workers mailing list, particularly by Jon Bell (until 2005) and Thor Kottelin (since 2007).
If your news server doesn't carry a newsgroup that you want to read, you may be able to read it from a news server that allows access from the general public (and not just its own customers).
Before you try to do this, you should be aware that many (or even most) so-called "public" servers are not intentionally public. It is fairly common for an inexperienced news server administrator to inadvertently configure his/her server so that outsiders can connect to it. Sooner or later he/she will probably notice it, and shut off outside access at that time. This is especially likely to happen if the server carries any alt.binaries groups, and most especially if it carries any alt.binaries.pictures.erotica groups. :-)
Most organizations that run news servers do not want usage by outsiders to degrade service to their own employees, students, or customers. Also, most organizations do not appreciate being used as a conduit for unsavory activities. Therefore, if you find a "public" news server that carries newsgroups that you want, please:
If you want reliable access to a large number of newsgroups, including binaries, then you should look for a commercial service provider that carries what you want, and pay for it.
Now that you've made it all the way through our sermon, here's a link to a possibly useful list of "public" news servers. James W. Abendschan periodically runs software that scans for publicly accessible NNTP (news) servers and creates a list.
Please read James' FAQ (Frequently Answered Questions) before using the list. Besides some of the same stuff you see above, the FAQ also describes how his list works, and its limitations.