If you want some 158 gr 357 loads that aren't full power, but are in 357 cases (no scrubbing the carbon ring like a 38 sp round), look for 357 ammo loaded with lead bullets instead of jacketed bullets..

There are factory lead loads that clock about 1,000 fps, which is at or just above 38 sp +P level. Should work great in your gun and be pleasant to shoot.