The Kanto, Johto, and Sinnoh legendaries don't appear in Sapphire. Sinnoh didn't exist when Sapphire came out, so, for the others, you had to trade between FireRed, Leafgreen, Ruby, Emerald, and Colosseum to get Articuno, Zapdos, Moltres, Raikou/Entei/Suicune (depending on your starter), Jirachi (from the Bonus Disk), and Mewtwo. Ho-oh, Lugia, Celebi, Mew, and Deoxys require Nintendo Events that are most likely inaccessible now. Regirock, Regice, Registeel, Groudon, Kyogre, Rayquaza, and Latios/Latias, however, can be found in your version. Check Serebii/Psypoke/Bulbapedia/Pokemon.com for more info. I hope this helps!
I have LeafGreen, Emerald, and Ruby. I also go to the websites I told you about often.