There are some nice brass cased rim locks around this period (some I’ve seem date from c.1720 to about 1830. They can have a dead bolt operated by the key, a spring bolt worked by the door handle and a slide bolt. These would be likely to have a key with a large Georgian (metal ring) bow. They are probably best looked for at antique fairs; perhaps some turn up on eBay, etc and you might consider a modern reproduction
Of course these old locks do not provide the degree of security now required! Around this period apart from iron rim locks, there were wooden stock or plate locks (the metal back plate that holds the lock mechanism for c1800 would to have a dovetail appearance).
