King's Landing hasn't been shot in Malta since season one. It's in Croatia now. And only certain exteriors for the city are done there; many King's Landing interiors are done on the sets in Belfast.
There's not a lot of Bronn in the first half or so of A Storm of Swords
, unless they're playing up the Symon Silvertongue thing (which I tend to doubt we'll see at all), but he's the sort of character the producers seem fond of, so I'm sure they've found something for him to do.