I'm rather curious about whether the different sources for stones have different rates or drop pools, apart from the 150% training ones.
JP wiki has some tables about the stones' sources:
[SPOILER="Summary"]
Most stones are listed as dropping in Alban Basic C rank (and potentially higher?), which I've abbreviated as Alb. Elite refers to shadow missions. I've included a bit of info from wiki comments I thought were interesting.
Yellow (difficulty):
Int - Alb
Adv, Hard - Alb/Elite
Heroic - Elite
One comment reports a Heroic stone from Shadow Wiz int, and another reports finding it in Alban Basic C despite the table data not listing missions as a source.
Red (party limit):
4, 6, unlimited - Alb/Elite
Comments: 6-player-stone reported from SCC elite, Unlimited from Conflict elite.
Green (player modifiers):
Talent 150% training - Adv/AdvHardmode dungeons
Everything else - Alb
Comments: Supposedly KR official site said the talent stones are only from Uladh dungeons.
Grey (monster modifiers):
All - Alb
Comments: 2x monster stone doubles miniboss spawns too, but not the alban golem. 70% spawn stone skips minibosses.
Blue (hidden floors):
Anvil, Gem - Alb
Halls - Alb/Elite/AdvHardmode dungeons
Comments: Warrior/mage hall stone drops reported in Enemy Behind elite. AAHM reported to drop warrior hall.
[/SPOILER]
As for how I'm handling it... in theory I should run the daily Alban runs and hope for good rewards. In practice, it fell off my priority list, unless I get stones from shadow missions I guess. Notably a heroic one.
Quote from UnclePine;1286819:
Do Enchant Expiration Removal Scrolls work on Alban stones?
Seems unlikely, but I tested with a gunslinger stone just in case. It didn't show up.