Many SE sites have a place for "community ads" on the right-hand side. SE Retrocomputing itself was promoted on SE Electronics (and possibly others.)
It can also be a place for non SE sites of potential interest. Again, on the Electronics SE, the famous EE Blog is often promoted, because it is of interest to the community there. I'm sure there are others, and it might even be a way to aggregate all those existing, but perhaps less visited sites we've bookmarked over the years.
As a suggestion for this site, there is a lot of retrocomputing stuff over on hackaday.com and the sister site hackaday.io.
Is this something we want to do for SE Retro? I recall it is as easy as having folks on meta present examples in the expected format, but I'm ignorant of the details.