There are a lot of blogs and websites dedicated to magical girls, naturally enough, but from what I’ve seen, most don’t stay active. A lot of them that I’ve stumbled upon look like legacies from Web 1.0, or haven’t updated for three or more years.
I did, however, recently come upon the magical girl wikia, which has possibly the most complete catalogue of the genre I’ve seen anywhere.
It has this partly because it’s decidedly generous in what it considers magical girl. Its timeline starts as early as the 1940s with titles like the film Down to Earth. I assume this is because they’re cataloguing the predecessors of Bewitched, which inspired the genre as we now know it.
It’s a good site. Go take a look.