Where do I find balsam?

[False Prophet]

I'm running low on healing pots and I would like to farm some balsam for alchemy

[SoloQ]

There's no way to "farm" anything really. Balsam is just found out in the wild of the surface world. You can also buy potions from vendors and potion ingredients from vendors. There's also a lot of potion ingredients all over the world randomly, like inside of crates and chests. And check the bottom left corner of the screen when chatting with people, some of them have the option to trade without obviously being a vendor.
And you can refresh vendor stock by resting until the next day.

[oncepostal]

Make sure to poke around any new camp/rest areas you encounter. Always finding one or two potion comps I didn't notice.

[Xenomorph Kitty]

Some vendors will also sell it too. Shop around and you should find some.

[TheGoblinPrince]

Just did some hunting myself and found some near the Risen Road waypoint, around where you fight the gnolls near the caves