yeah, apparently sometimes less popular villagers are even harder to get than popular ones just 'cause no one ever seems to have them. Or so I hear!
Having a cycling thread would almost certainly result in less voided villagers, but I've never set one up myself so I don't know any good ways to do it haha. xp
It's faster and easier to do it the way you are, just posting a selling thread when you get a popular villager, but if you did want to adopt out more then making a cycling shop would be the thing to do. One of my personal favorite cyclers is Zulehan (thread here) if you wanted an example of a thread layout. I think he recently had some bad experiences with people who got mad at him when they didn't get the villager they wanted, if you're wondering why his first rule sounds so strict. hehe