On a new day, you start a new character and check your campsite. If there's a tent/igloo there with someone you like, plot and save. Then you're free to adopt that villager if you wish. If there is no tent or the villager camping is someone you don't want, quit and repeat until you do find someone. It's incredibly tedious and you're much better off adopting someone on the trading forum.
you could do a campsite reset trick. its similar to plot reset in a way. just TT a few minutes before 6am with your existing characters and then create a new character. proceed to check campsite if theres any campers. if no, create a new character again and check again.