Adamant is not a good nature for Salamence. Salamence is designed to be a mixed sweeper or a D Dancer.
Natures to avoid for Salamence:
Adamant
Brave
Bold
Impish
Relaxed
Modest
Quiet
Calm
Careful
Sassy
Timid
Jolly
Lonely, Naughty, Mild, Rash, Hasty, or Naive are the best natures for Salamence(ATK/SA/SPD+, DEF/SD-)
Actually, Adamant sucks more than any -- it blocks Salamence's necessary Self-cover (Flamethrower-self cover vs Ice)
If you insist on using Adamant, try this
D Dance
AA
Brick Break
Dbl Edge
A Phy sweeper to take what little advantage you can from Adamant nature.
For an item, Scope Lens maybe?
From my simulations, Scope Lens>Choice Band. Scope Lens increases Critical Hit ratio. CB prevents you from using three of your moves with a power boost for the fourth.