Don’t exactly know the best way for this to be made. I’m guessing a special page built into the platform might actually be the best way. It’d just provide a list of all communities the instance federates with in order of ascending age.
Or, maybe more easily, an admin run community for people to post about their new communities?
This post is better suited to !lemmy@lemmy.ml
Please consider moving this question to there instead, where staff are more likely to see it.