There's a store in Pittsford along the canal (tucked back behind all the Schoen Place stores) that is all dollhouse supplies - they may have kits.
Then there's this crazy expensive place
in Fairport. I've never been.
If you have any interest in building a log cabin dollhouse, I have a kit kicking around that I'm never going to get around to building.
And, as always, garage sales are your friend. I got this enormous one
for $30 last summer, complete with a lot of furn worth quite a bit of $. I keep running into dollhouses for sale this way and I don't have the money to buy them all! Also try the Avon Flea Market and the Rochester Public Market on garage sale sundays. I'd seen some both places last year.