I would keep an eye on local ads, charity stores, auctions etc. I'm sure there are a pre 1900 machine near you, they usually turn up now and then, even if not as plentiful as the later ones. You are not going to find a sewing machine as old as the house, and if you plan to actually sew on it, I can't see any good reason not to get a model that works well and one of the great successes; with still reasonably easy to find bobbins and needles. A treadle would be as good a choice as a hand crank, maybe even better. A house always have a history much longer than it's first few years, it's important to take care of all of them, especially when what's lost really can't be saved and what's been added is worth taking are of :- )