How does one get a sharpedoite and a galladite in ORAS

The chance of an egg being produced is dependent on the Original trainer ID numbers and Species of the pokemon involved.

The day care Man can tell you how likely an egg is going to be generated after each set of 256 steps going on what he says.

Taken from Bulbapedia:

• Same species, Different Original Trainer - "The two seem to get along very well" - 70% (88% with oval charm)
• Same species, Same Original Trainer - "The two seem to get along" - 50% (80% with oval charm)
• Different species, Different Original Trainer - "The two seem to get along" - 50% (80% with oval charm)
• Different species, Same Original Trainer - "The two don't really seem to like each other very much." - 20% (40% with oval charm)
• Different Egg Groups, same gender, or Undiscovered group - The two prefer to play with other Pokémon more than with each other. - 0%

That's all there is to it. It didn't need to change as the generations went on, they've just added more mechanics into it, like IV and nature breeding.

Yes, the Shiny Charm is available in OR/AS, and the method to obtain it is the same as in the previous two games. You must first complete the National Pokédex, and then speak to your game's Professor (Birch, in this case). Completing the Pokédex in this context does not require you to have obtained any of the event distribution only mythical legendaries. You might need to progress the story to the point where the Regional Pokédex is upgraded to include National Pokédex.