How do you get Sonic 3 and Knuckles on Sonic Classic Collection?

It's already there, Sonic the hedgehog, Sonic the hedgehog 2, Sonic the hedgehog 2 and Knuckles, Sonic the hedgehog 3, Knuckles in Sonic the hedgehog 3 and Sonic and Knuckles are all the games that are in Sonic Classic Collection, they are available straight away.