Where is Aurelion Sol?

They don't release champions the moment of the patch. Not anymore at least.

{quoted}

He's still planned to be released this patch! No definite date/time yet, but, generally speaking, it's become standard practice to enable new champions a few days after the patch is already live so that we can be sure there's no technical problems with the patch.

If you read the patch notes you'd see the "Will be released sometime later this patch" note they always throw on the Champion releases these days. He'll drop sometime within a week of the patch unless we get unlucky.