I just noticed someone made an effort to hunt down every blosxom plugin ever (seemingly ever) and stick them in one Github repo.
The current official site for Blosxom has a long list, now filled with 404 errors, but not as long as this one. I see someone else wrote a tags plugin, unfortunately the documenation for that appears to be in Japanese, so I can't be sure how it works without studying the code. There are also a few commenting plugins. I will be looking at those, too.