Find the Dungeon of the Decayed and its stela. Save there so you can do some quick loading

Just go right, break the armor display, and hope you get a piece of armor full of runes.


Re-load the file when you don't get it.

Really the idea is just to find a save point with an armor display nearby, for which I've found one or two of throughout the rest of the game, but I can't remember them specifically. They probably drop armor as well? I haven't been paying attention to those.
Maybe there's some other place with multiple armor displays near a save point, but I don't know 'em.