The newest adventures do NOT classify as distant lands and will not drop sun stones
Search the Ancient Vault, Hunt Roaming Bandits and Explore Dark Caves all dropped from 5 to 15 stones.
Traverse the Desert Sands consistently dropped over 20 stones
Feral Lands Adventure and Envoy to the Plume Hive did NOT dropped any after at least 2 tries
Dragons and Manticore obviously dropped Sunstones, I have gotten over 6 by a single dragon