Or indeed on G+ or GooglePlus. Anyway, having made that point too often, I'll move on. One of the disadvantages of G+ is that it doesn't have a decent search option inside it. There is a search option, but it's really only for use with people and their names, rather than for subjects. In order to search G+ content you have to get slightly creative with Google itself.
You have to start off with site:plus.google.com which tells the search engine to just search that site. Then we want to add in librarian - it's intelligent matching should work out library, librarians etc, or you could force the issue with ~librarian to get it to search around the subject a little more. This then brings up a bunch of results which include people who have posted about the subject. So to exclude those add in -"post by" and you'll end up with your string
site:plus.google.com ~librarian -"post by"
Obviously you can replace 'librarian' with anything else that takes your fancy. What Google appears to be doing is searching through the profiles section. This mainly pulls up people who are current librarians, but also has a few false drops from people who were, and are no longer. You can of course leave it at that point if you want, or add in more terms. However, if you want to get really insane, you can start to create your own circle(s) of librarians. Please bear in mind however, that when you start doing this with Google the results count does actually go haywire - you're never getting accurate count and this changes with frightening regularity.
However, I started adding librarians - or people who identified themselves as librarians - to a 'librarians' circle this evening. The only exception that I made was to exclude anyone who was exclusively writing in a language that I couldn't understand. Sorry and all, but it's my list and thems the rules. 2 hours later I had almost 300, which isn't bad so far. I was then able to post to the list, explain who I was and so on. Now, I'm going to want to check this on a regular basis, so the next step was to keep a note of what I'd not looked at.
I have two options here - I can set up an email alert. Go to Google News and type in any search that brings back results. Then scroll to the bottom of the page and click on the 'create an email alert'. When you get into the option replace your fake search terms with the one given above. Then choose your delivery options and you're done. I couldn't get the RSS option to work at all though, so I'll work on that a bit more.
The second option is that once you've run your search, simply wait a while and run it again. In the left hand menu click the option to view 'Not yet visited' results. That way you should hopefully just get the new stuff. However, once again, Google isn't too clever. The first time I ran my search I got 3,150 results. Limiting my search to pages that I've not visited, but actually the number increased to over 10,000. Irritatingly, it did pull up some very useful results. However - when I first ran the search to create my initial list Google told me I had about 750 results. After 30 pages it then told me that I'd reached the end of my search results - not terribly accurate. So are there 10K results? I have no idea.
If you do decide to create a huge circle in G+ you need to appreciate that your Stream very quickly becomes a random mess of stuff - think Twitter without the 140 character limit. This many people is going to wreck your stream totally. It's a shame that we can't yet limit results to a specific circle, or to share circles to create mini groups. However, that you can't properly use your stream isn't a big deal, since you'll probably be spending most of your time in one or two circles chatting with friends and colleagues.
Right... I'd better get back to finding more librarians to add. If you are a librarian and are on G+ and I've not added you yet - please feel free to add me to a circle and I'll get back to you.