How to efficiently obtain Rumi's Concoction as SSF?

Granite flasks don't drop in large quantities. And so, it's a bit harder to get a specific unique granite flask (Rumi's Concoction) than for many other items because chancing one is relatively unlikely. At the very least a scouring orb is needed for almost all chance orb attempts.

There is a vendor recipe for granite flasks, which could then have a chance orb used on them. But, producing each one takes quite a few alteration orbs to get the right suffix on each elemental flask used in that recipe.

I know about a couple of resources other than chance orbs ...

1. Create a unique flask (Beastcrafting)
2. Sacrifice a unique item in Temple (better chance for higher tier sacrifice rooms).

... and I'm not sure what else might be done.

Any insight others might have would be most helpful and appreciated.

there is a div card for a unique granite flask. theres only lions and rumis, so your odds are pretty good with that.

Earth Drinker -

https://pathofexile.gamepedia.com/Earth_Drinker

You can also Chance a Rumi if you need. Either a Rumi or a Lion's Roar will come out from chancing Granite flasks.

You can combine a Ruby, a Sapphire and a Topaz flasks, all them with the "of Iron Skin" modifier at the vendor to get a white Granite if you find a shortage of them

Thror2k5 gave you, actually, the only, faster way you have instead of getting that flask. Other ways are going with Jack-In-The-Box, which drops a bit more often than Earth Drinker, or keep farming Elreon or maps with Unique Delirium Orbs and Reliquiary Scarabs.

Beastcrafting too is a good way to get a Rumi, expecially if you can keep the beast's level low (lower item level means less chance to get a wrong flask).

Of course, Ancient Orbs are a thing too, if you happen to have a surplus of them.

Excellent news!

Thank you for passing this along.

Farm Desert and Dunes maps for "Earth Drinker" cards.

just chance it.....don't know the drop rate of the card