… and in that last post, I completely neglected the point.
The point is that in these hierarchies of puissant beings, they end up using magical items the same way that mortals do. And as a result, they end up having spare magical items as surplus, as arms dealers, as cultural exchange tokens.
While it’s still a little hard for me to say that a mad wizard in the boonies has a “magic shop” where they have Excalibur hanging behind the counter, it doesn’t seem at all mad that the Caliph of Ash, Lord of Efreeti, has a scroll of cone of cold he’s not doing anything with.
So: when your characters start hitting max level and want to buy better magical gear, they absolutely should be seeking out the Three Great Cities, the City of Brass (Efreeti), the City of Iron (Devils), and the City of Silver (Angels).
They should find an elven prince and do them a great favor. They should find a druid hierophant. They should find a grandmaster of assassins. They have storehouses, and probably need allies: the gold is probably not the point for some of the more abstract entities, but instead the idea of wealth (especially Iron and Silver; Efreeti probably like metal for metal, but Devils just like knowing how much it’s worth to you).