Unless you're specifically looking for a physical product, you could probably draw what you need from a5e.tools site, but honestly I'm not sure the stronghold rules fit with "kingdom style" play precisely. They're more like an alternate magic items system with a roleplaying hook.
Though to be fair, I've never really understood the domain management concept as a game. Even in versions of D&D that in theory support it, it's never seemed to me that there's a lot of rules actually governing activities at that scale.