http://www.earlyrusticarms.com/pricesanddescriptions.htm Early Rustic arms might be a place to look. Since you're looking for quality I believe. These would have some of the better quality locks and barrel and produce you excellent accuracy, exceptional style, and value. They might be a little more then you want to spend depending on how nice of a rifle you want to move into and it take a while to get the rifle produced since these are all hand made.
You could also look at
http://www.rmcsports.com/catalog.htmRMC Sports. He makes an excellent rifle with a Green Mountain Barrel, Davis lock, and his flintlocks have a removable breech plug for easier cleaning. The are real fine rifles as well.
There is of course the Lyman Great Plains rifle with the 1-60 twist which will be a great shooting roundball rifle as well as an excellent hunting rifle. Lyman makes a good lock and their accuracy is excellent as well...
Just a few places to start looking.. Good luck in your search.