They need to add Pandemonium events, seek out unique monsters that spawn randomly throughout the world and have a chance to drop keys. Once you get all the required keys, you get one portal to Greed's Realm. Inside of Greed's Realm, there is hordes of treasure goblins and the boss himself, Gheed!
Edit: Or just have goblin's randomly drop keys since they already randomly spawn and can be tricky to kill sometimes
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