If the flange on your recoil spring cap is as heavily peened as you describe, I would advise that you check your slide stirrup and the recoil boss in the frame. If they're not square to the centerline of the gun then they're going to peen the flange again no matter what springs you use. The Seattle guns got out the door quite often with "as cast" surfaces which were usually not smooth, nor squared to the centerline.
One thing the Seattle guns did have was good springs. (So does the new company, by the way). I doubt if many Detonics owners will ever wear them out! The average gun owner never gets more than 5,000 rounds through his piece. As such, the springs may take a set, but they'll still be good.
...Deeton