What is the difference between a published and unpublished TFR?
It looks like you have two questions: what's an unpublished TFR, and where are NOTAMS published?
First, unpublished TFRs. I can't find any FAA information on &quot;unpublished TFRs&quot; and I suspect it was just poor phrasing from FSS. I read the article you linked and it's unclear what they really meant, at least to me. Having said that, you could interpret &quot;unpublished TFR information&quot; in two ways:

Unpublished information about TFRs
Information about unpublished TFRs

I believe the intention was #1. There's a blanket 'stadium TFR' NOTAM but it doesn't include key information, like when the TFR is active for a given stadium. That's because games schedules change and the FAA doesn't keep track of them; it's up to the pilot to know if there's a game going on or not. For that reason, the stadium TFRs are very unpopular with pilots.
But, FSS might still tell you if a stadium TFR is active. Especially for major, high-profile events like the Super Bowl. There's no guarantee that they can or will, though, especially since FSS has become more centralized and less local.
Second, NOTAMs. The FAA currently publishes them here: https://notams.aim.faa.gov/#News
I say &quot;currently&quot; because the FAA seems to like moving things around and breaking links. But as you can see from that site, you can search yourself and there's also an interface that other systems can use.
Finally, that brings me to the practical answer to both your questions: just use your favorite flight planning app. I use Garmin Pilot, which displays current and future TFRs, and it keeps track of sporting event schedules. It also has NOTAMs, of course. Foreflight or other alternatives would do that too, I'm sure.
The stadium TFRs are usually easy enough to work around because - except for really big events like the Super Bowl - you can fly through them anyway if you're talking to ATC. So if you can get flight following (always a good idea) then you're complying with the TFR requirements.