[This couldn't be more perfect. So very lucky]

There is an apothecary-come-alchemist that stocks it, in the Fifth District. You'd better hurry though, supply is limited.

[He just about resists the urge to wink at her, it feels pretty good to have managed to sell it to her, even though it'd been under duress from Barkeep.]

You might get a discount, if you mention I sent you.

[....unlikely, but not impossible to believe given how much of the stuff he's bought from there over the last two years.]