Niederlander
To properly answer, I gotta ask a couple of questions. What specific gun are we talking about?? Colt SAA?? Colt SA Replica?? Uberti or Pietta?? and do you wish to modify the frame??
I am actually, on second thought, thinking you may be enquiring for a Colt SAA. If so, My recommendation for a Trigger/Bolt spring would be the Pietta SA trigger bolt spring. The Pietta is well designed lighter flat spring that is not prone to breakage.
When it comes to Hand Springs, unless you are willing to drill the frame for Coil Spring and Plunger, then modify the hand for same, there is actually no "really good" flat hand springs. They are all somewhat flimsy and prone to breakage. If you are replacing the Hand Spring for a Colt, I think flat hand springs are still available from Uberti??
Play Safe Out There