Istani/Kournan Chests

Does anyone know the location of one of the above chests, ideally near a portal?

I have been aimlessly running around for ages trying to find one

All chests except the Treasure Chests (which can only be opened once per month) are random for spawn location. There are AREAS they spawn in more often, but there is never a gaurantee for finding one.

even though random, somehow you get a chest just outside boreal 90% of the time.

Note that the algorithm generating chest spawns EXCLUDES the spawn locations nearest to the portal you have entered the zone with. So even if there's a common spawn location near a portal, you will never get a chest to spawn there if you entered the instance by that portal.

It's all distance-based, so chests start appearing normally in a distance of above 1.5 radar radius from the portal, as seen for example outside Boreal Station.