In ORAS, where can you find Gastly?

Question

I just need to find where (If you can) Gastly or it's evolutions.

Answer 1

Gastly, Haunter, or Gengar cannot be found in ORAS.
To get it, you will have to trade.
If you have another 3DS and Y/X, you can find Haunter on Route 14, Route 19, Victory Road, and Frost Cavern.

Hope I helped!
Source

Answer 2

In order to get Ghastly in ORAS, you need to breed a Haunter or Gengar in Pokemon X and Y, then you can trade it over to ORAS because you are unable to catch Ghastly or any of it's evolutions in ORAS.