It's very time consuming to get the villagers what you want; I just do it because I don't use Bell Tree as a tool for obtaining villagers or items through buying/selling.
Basically, when I have 8 villagers, I time travel. It's pretty much just a process of
1) Time travel one day forward.
2) Create a new character
2) Check to see if there are any villagers plotted.
3a) If there is not a villager plotted, go through all the steps of getting a house on the new character and saving and then deleting the new character. Then TT forward another day.
3b) If there is a villager plotted but it's not what I'm looking for, simply press home and exit out of the game
without saving on the new character.
4) Repeat the process of making a new character, saving when no villagers are plotted, and TTing one day until there is either a very highly likely chance or 100% chance of a villager plotting. Day by day, I believe the % chance of a villager being likely to plot goes up when you do this. It's noticeable after you do it for a while. Once you have pretty much a 100% chance of a villager plotting on one day, you won't need to TT forward anymore. You just create a new character and quit without saving each time that a villager you don't want is plotted (or actually do save if the one you want is there). This method works because plots are set in stone if you load up your mayor, but new characters the villager will change each time since the game doesn't auto-save once you make a new character.
I hope this makes sense. I'm not very good at making guides. Honestly, though, this process is very tedious, despite being how I got all of my dream villagers for my main town. I wouldn't say I'd recommend it, I'm just hard-headed and refuse to do any kind of Bell Tree trading. I'm in the minority on that subject, so I would definitely recommend just going the Bell Tree route. It's so much easier to just buy a villager off of someone on here!