Oh, I'm gonna guess you're new to pokemon training, as I am new to this forum (kinda xD)
Getting a different nature isn't that hard, you just need to go ditto hunting first for a bit. Try to get a ditto of every nature. Then give that ditto an everstone and breed with your Salamence(which you can't use in competitive play no more since it's uber according to smogon) and you have a 50% chance of salamence having dittos nature. As for IV's, they don't really matter that much(for a salamence anyways), so don't worry about it.
As for EV training, don't bother with EXP share. Give it the item it needs to raise up it's EV's. Put him in the front, go into a battle with your target pokemon, and switch out to a higher level pokemon and kill it off. After you've gained all 510 EV's(you have to keep count), use the same method on the elite 4 to level up.