Leystone Ores was introduced by the Legion expansion of WoW. There are two places that is actually decent to farm Leystone Ores. Have a look at the maps below for the routes to farm Leystone Ores in wow.
If you are lower level and you want to farm for Leystone Ores, then you should slay and mine Lagoon Basilisks in Azsuna just north of Narthalas Academy.
If you are at a higher level then this map might suit you better. The route is at Sarumar.
Hope is helped you with farming Leystone Ore in wow.