If you are seeking a "best quality" hammer gun you might look for one from Purdey, Holland & Holland, Boss, or one of the other old-line English makers. Otherwise, you might consider a lower-grade Parker, Remington, or L.C. Smith.
You will find some offerings fitted with Damascus barrels, while other, later models, will feature nitro-proofed Whitworth Fluid Pressed Steel barrels. If money is no object you can have the Damascus barrels on the gun of your dreams sleeved so that they may be safely used with modern nitro-powder loads. Whatever you choose, for safety's sake please have it thoroughly checked (paying particular attention to the barrels: no bulges, dents, or excessive pitting or corrosion) by a competent gunsmith before you part with your hard-earned brass.
I have a L.C. Smith Field-model hammer gun with fluid steel barrels. It's nothing fancy, but I love it because it is solid and reasonably well-made, and being afield with it puts me in an Edwardian frame of mind (sort of like being in an A.B. Frost painting come-to-life).
Good luck, and good shooting!