There are actually only a few breedable Pokemon with unreleased HA. The ones I can remember are Johto & Unova starters, as well as Skrelp, Tyrunt, and Amaura.
However, if you want to go into detail, there are other things to consider.
For example, the game where the female parent originates from. A female parent from Kanto/Johto/Hoenn/Sinnoh cannot have an offspring with HA, since she cannot legally have HA.
Then there's also the ball.
Pokemon in Apricorn/Sport Ball cannot legally have HA, since it or the mother would have to come from HG/SS.
Pokemon in Safari Ball also cannot, as it or the mother would originate from Gen 3 or Gen 4 game, where HA does not exist yet.
And then there's a unique case with DW Kecleon, which is from Gen 5. Kecleon didn't have HA in Gen 5, but it has one in Gen 6. However, when a DW Kecleon is transferred to Gen 6, its Color Change ability doesn't change into Protean, likely because of the way Kecleon's ability is being set in Gen 5. Therefore, it's actually impossible to get a Protean Kecleon in a Dream Ball.