There's a spot in highmountain, shipwrecks cove (48,7), that has what seems like bugged spawns. They're easily missed as they're not poking through the ground in the shallow water and most people don't stop to take the few seconds to mouseover. With that in mind, you can simply stand in this spot and mine either felslate or leystone (whichever spawns) and simply server hop. No aggro from the mobs nearby, seems easily bot-able if set on a timer to server hop. seems like about a 70% spawn rate on that exact spot
I personally am a miner and herbalist, so there's many other nodes in the are that can spawn too.

Here are my results for an hours worth of work
Felslate x 182
Leystone x 248
Foxflower x 139

here's some screens if there's any confusion (they're not the best, but you'll get the idea)

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