Reasons to be Cheerful was founded by David Byrne to make more good news in the world. Would be a good source of articles for a “good news” community.

There are a few different resources available for searching communities. One is sub.rehab, which tries to match up subReddits with various replacements. Looks like there isn’t one for r/BuildaPC yet on there.

The other resource I use is Lemmyverse which has a lot more data. Looking there, it appears there are several buildapc communities.

If you are wondering how you would follow those, if they aren’t on your server, you take the full name (ex. !buildapcsales@lemmy.ml It’s similar to an email) and search for it from your server, then subscribe. Once you do that, the server will fetch posts from there automatically for both you and anyone else on the server if they’re subscribed or looking at all. Hope this helps!