Alright, this is going to be a lengthy one, so prepare yourself. I've had trouble finding this info in bits and pieces across the internet, so I've tried to include everything in one post here. (If you just want odds numbers, go to about the midpoint of this post.)
First off, I highly recommend getting a destiny knot, as it is essential in breeding for IVs. In ORAS, you can get one either in Sea Mauville by chance after beating young couple Lois and Hal (you can save before the fight so you can reload if you don't get the drop), as long as it's not your first time fighting them. You can also get one by chance after competing in a master rank Pokemon contest and talking to your fans in the hallway, though I'm not sure on the exact odds for either of these.
Anyways, in order to start transferring IVs to the skarmory of your choice without using a ditto, you're going to need a female skarmory, which is a 50/50 chance in the wild. The more perfect IVs on the female, the better. I recommend chaining with the pokenav since it tells you if you've found one with at least 1 perfect IV via the stars. I'm sure you already know all of this, but I figured I'd include it regardless in case it helps out any future readers.
Once you have your female skarmory, the long and arduous process of breeding for IVs begins. This is where we take a look at the odds of things happening favorably.
For every perfect IV each parent has, you have a 1/12 chance of passing down a perfect IV to the egg. The reason it's 1/12 and not 1/6 is because it takes those IVs randomly from both parents, and if only 1 parent has a perfect IV in a particular stat, the chance of inheriting it comes down to whether that particular stat is going to be inherited, and if so, which parent will pass down their inheritance. With regular breeding without items, this maxes out at 3 possible inheritances. With a destiny knot, this becomes 5. Any IV produced outside of inheritance is rolled at random, with a 1/32 chance of producing a perfect 31 IV. (Yes, the odds are 1/32, not 1/31, because 0 counts as a number when it comes to IVs, and 0-31 is a total of 32 numbers.) This means that any random stat has a 3.125% chance of being perfect.
What this boils down to is, the more perfect IVs that can potentially be passed down through inheritance, the better your odds of producing a perfect offspring.
If both parents have the same perfect IV, then if that IV is inherited, it is guaranteed to be perfect. Luckily, there are items that can help with that; the power items that you can get for BP in the battle resort. With these items, you guarantee that a specific IV gets passed down, reducing the random chance of inheritance by 1 selection, which helps increase the odds of producing better offspring. Do keep in mind that the battle item does not add an additional inheritance on top of the 3 or 5 regularly passed down, but simply locks one of those into a certain stat, leaving 2 or 4 left to random chance, respectively. No matter what you do, there will always be at least 1 stat left completely up to chance.
~~~Data segment~~~
So let's take a look at some data.
For each IV to be passed down by chance without assistance, there is a:
8.33% chance of getting each perfect IV to pass down.
16.67% chance of passing down each perfect IV that both parents share.
3.125% chance that each remaining IV will randomly generate a 31.
What this means is that, at best, your chances are about 0.00000014% to randomly get a 6/6 using this method, or 1/140,000,000. Ouch, that's a lot of eggs. Not to mention that, assuming each egg takes roughly 3 minutes to hatch, you're looking at 7,000,000 hours spent hatching eggs, or nearly 900 years. So in short, not exactly viable.
When using a battle item to guarantee 1 perfect IV inheritance, the other inheritance odds go up slightly because it takes one random chance out of the equation, which then makes the odds:
10% chance for each unshared perfect IV.
20% chance for each shared perfect IV.
each remaining IV still only has a 3.125% chance of randomly generating a 31.
So in order for an egg to produce a perfect Pokemon using unassisted breeding, even with optimal odds assuming you score 3 perfect inheritances and ignoring the odds of having to get the 3 perfect IVs, you're chances are about 1/32,768, or 0.003% Pretty rough. Still, you should get one in about 4096 hours of non-stop game time using this method, which can still potentially happen within your lifetime.
However, the more perfect IVs you're able to add to the mix, the better your odds get. And with destiny knot, the odds can get much higher.
Personally, I find going from 5 IVs to 6 IVs to be the biggest hurdle, and I've got some data below to show why.
Let's say you manage to score 2 skarmory with 5 perfect IVs and you're breeding for that perfect 6/6 using a destiny knot. If both parents had different imperfect IVs, the odds would be roughly:
75.1% chance to get 3/6 IVs.
19.3% chance to get 4/6 IVs.
6.4% chance to get 5/6 IVs.
0.2% chance to get 6/6 IVs, or 1/500. Roughly 1 every 25 hours.
If the parents shared all 5 perfect IVs, the odds look more like this:
91.75% chance for 4/6 IVs.
8% chance for 5/6 IVs.
0.25% chance to get 6/6 IVs, or 1/400. That's 1 every 20 hours or so. A bit of an improvement.
Now, if we add a power item to the mix to guarantee a perfect IV from those same parents, we get:
79.44% chance to get 4/6 IVs.
10.24% chance to get 5/6 IVs.
0.32% chance to get 6/6 IVs, or 1/312.5. That's about 1 every 15.625 hours. Yet another improvement.
Unfortunately, this is as good as it gets until you manage to score a 6IV. Once you do, all of those odds effectively double in your favor, meaning you go from 1/312.5 to 1/156.25. These numbers also assume you don't care what gender the 6/6 comes out as. But if you're breeding something that has a ratio similar to Eevee's ratio of 1/8 being female and you want a female, then that just pushes your odds from 1/312 to 1/2496, or 0.04% chance even with optimal odds. That still doubles if you have a 6IV though, boosting your odds to 1/1248, or 0.08%!
The good news is, once you have two 6/6 breeding Pokemon, then you will get a 6/6 much, much more easily, with your odds at a much more manageable 1/32, since you'll just be relying on the random roll of the last IV to come out to 31.
I really hope this big dump of information helps in some way! Note that these numbers are universal in any mainstream Pokemon game that allows breeding, and are not exclusive to ORAS. All time estimates given are using an average hatching time of 3 minutes per egg. Good luck to future readers interested in the breeding process as well!