I'm looking to try to obtain more Master Balls to make Legendary capturing a bit easier. Is there any way to do so without a duplication glitch?
Yes, there are three ways to get Master Balls in ORAS, excluding the one you get during the story.
It is possible to get a Master Ball from a Secret Pal when you ask them to "Pick something up"
Matching all 5 numbers at the Pokemon Lottery Corner
Playing the PokeMileage Club game "Mine Cart Adventure"
Hope this helps!
If I'm not mistaken, you should be able to make one of your Pokemon hold your MB, then get in a double battle and have another Pokemon use Thief on it.