So, I did a calculation. Out of the 719 currently officially known Pokémon, 246 are unavailable in Pokémon Omega Ruby & Alpha Sapphire, so they have 473 Pokémon in them.
Conversely, X & Y have, out of the 719 currently officially known Pokémon, 127 unavailable, so a total of 592 in them.
Between them, there are 706 Pokémon available and 13 that are not. These are the Mythical Pokémon: Mew, Celebi, Jirachi, Phione, Manaphy, Darkrai, Shaymin, Arceus, Victini, Keldeo, Meloetta, Genesect, Diancie.
Out of those, the following have had events in Gen VI
Celebi (Worldwide - Pokémon Bank)
Jirachi (Korea (Movie Event), Japan (Tanabata Festival, Christmas Gift)
Darkrai (Japan - Movie Event)
Shaymin (Japan - Pokémon Scrap (from next week))
Victini (Japan - Pokémon Scrap (from next week))
Keldeo (Japan - Pokémon Scrap (from next week))
Diancie (Worldwide)
This means that 713 of the 719 Pokémon are available with the blue pentagon. (Phione can be bred from event Manaphy and have the blue pentagon)