you seek a 'hassle free' flintlock, and this is a good thing, but you should go into this project with eyes wide open ...
hassle free is a pretty 'relative' term ... remember that (1) this isn't you basic deer rifle, where you shove a cartridge into it, close the bolt, pull the trigger and it goes bang; all flintlocks, even very good ones, will require some adjustment and tinkering for optimum performance ... and (2) there will be a learning curve, where the rifle will show you stuff and you will show the rifle stuff.
many of the flintshooters started out with a Great Plains style rifle (think "Hawken," but without the subtle architecture - putting a chrome kitty on the hood don't make it a jaguar) you may find some very good deals if you look at Thompson Center or Lyman, both of which are pretty reliable.
check out the 'classified' section of this site - you can find some reasonably priced stuff.
also check out Dutch Schoultz' method, here:
http://www.blackpowderrifleaccuracy.com/
this has some great tips and tricks, and if you use his method, your groups
will shrink.
good luck, and make good smoke!