Oathkeeper
"Wait!" he says, do I look like a waiter?
I don't think there's one specific place that has them all. Each tier may or may not have their own "Good Cores" thread in their respective forum. I know PU does right here: https://www.smogon.com/forums/threads/ss-pu-good-cores.3664886/Where can I find the cores page for each tier?