Read an austen or two. Q hates them, but they're not all that bad.
Memory (and a poke at google) tells me that you might find some of the shoujo rpgs or semi-systems to be useful (Heartquest (fudgebased) is the one that seems most polished, but I really can't speak to any of them). You'll have to rename some things, but a system built for shoujo rpg (assuming it doesn't assume mahou shoujo) should be able to simulate regency romance with no systemic changes at all.