Question

How/where do I get the life orb in ORAS?

Answer 1

You can get the Life Orb from Battle Maison for 48BP.

Or, you can use the DexNav and find one on an Absol.

Source: Serebii

Answer 2

Life Orbs can be obtained:

1. At Battle Maison for 48BP (post-game only)

2. Held item (5% chance) on wild Absol. Wild Absol only appear on Route 120 at a 5% encounter rate, so it's very rare to find this held item. If you catch an Absol first then you can use the DexNav feature to encounter more of them faster.

So the only way to get a Life Orb pre-E4 is via wild Absol. DexNav helps a lot, and if you can build a farming team with Compoundeyes/Frisk/Thief that will make things even easier.

Source: Guide Strats