As I said, to try and find the Middletons and start an acquaintance with them, they would have to visit Exeter on a regular basis. Unless they were lucky and met Sir J and Lady M on their first attempt, it migth take weeks before they managed to find them. Since their friends are probably not that well off, its unlikely that they are mixing with the sort of circles that Sir J woudl be in, and the only way teh Steeles could find him would be to hang around or stay in inns where upper class people might be staying on a short visit or keep hanging around the fashionable shops.. that woudl take time and money. It would also look pretty odd IMO if Lucy and Anne were staying at an inn and enquiring however discreetly to find out if a married man like Sir J. often stayed there. It might make htem look like ladies of dubious virtue. So I conclude that the Steeles weren't looking for the Middletons.. they were just visitng friends in Exeter, happened to meet Mrs J and Sir John possibly at a fancy shop and managed to find some distant relationship between them.. which led the kindly pair to invite them to Barton and having a better invite than their friends in Exeter, they took the better invite.. I think that the fact that Barton happened to be hte place where teh Dashwoods were living was just a lucky stroke for Lucy, as it meant that in additon to having a comfortable place to stay, she could find out more abuot the Ferrars family and about this Elinor that Edward was talking about...