Is my team obtainable before the postgame?

I was about to start a new save of Omega Ruby and I was wondering if the team I chose was obtainable before the elite 4 and the post game

Team Pokemon Omega Ruby

• Swampert (Starter)

• Gardevoir (Route 102)

• Breloom (Petalburg Woods)

• Gyarados (Route 102, 103, 104, 105, 106, 107, 108, 109, 110, good rod)

• Magnezon (Route 110, evolve in magnetic field)

• Salamence (Meteor Falls)

Only Swampert can get his megastone before the postgame right?