I have a Merit optical attachment instead of a peep sight. It is essentially am aperture sight that mounts to your glasses with a small suction cup and attached to the suction cup is an aperture sight that can be adjusted to your eye. I bought it for handgun hunting because I didn't want a scope on my Ruger Blackhawk .45 Colt. It works well and is less expensive than installing an aperture sight on your Flintlock rifle.
http://www.midwayusa.com/product/978...th-suction-cup