I have a Left hand Lyman Great Plains flint rifle in 50. It's great. I've had no problems. I bought it used online and have no idea of it's age or use, but the lock has never failed me and it sparks well. (I have two rifles with Jim Chambers Siler's so I know a good lock, and the GPR is fine, in my opinion.)
I have taken two deer with this rifle. My only complaint is that it is heavy.
If you want a Hawken style that is more historically correct with flint, you might look into a Lehman style rifle from TVM. . .but it is full stock. . . you'll have to wait a while while it is built as a custom rifle. I have their late lancaster and they make a very fine rifle.
Most shooters, however, don't know historical accuracy . . . most modern shooters look at my muzzleloaders like a cow looking at a new gate no matter what model I show them . . . so if you like the Lyman, that's what matters most, in my opinion.