You can hire alchemists to brew custom potions. (Potions of Climbing and Potions of Healing are the only "standard" potions you can easily buy.)

The amount of available alchemists depend on the city population size (Hawa has 1d3) but they're all equally good/bad. They need roll 12+ on d20 to succeed with a brew attempt and if you can save against the potion, the DC for those saves is 14.

They already have the recipe to brew potions corresponding to all level 1, 2 and 3 wizard spells.

For potions corresponding to spells from other classes or from other spell levels, they need to research the recipe.

This includes custom spells that doesn't even exist in 5e! We'll have to figure out what the spell level would be by comparing to existing 5e spells.

The price for inventing a new recipe is 500 dinars per week and it takes [spell level × 4] weeks to make an attempt. The alchemist must roll 12+[half spell level] or higher to succeed in finding out the recipe. They'll know right away whether the recipe is legit, there's no recipe that looks like it'll work but then won't.

Then, once they have the recipe, the price for brewing one flask is 500 dinars per week and 500 xp worth of thematically appropriate monster parts (for example troll blood for a potion of healing) per week. It takes [spell level × 2] weeks to make an attempt. They must roll 12 or higher to succeed in brewing. Again, you'll see right away whether it was a good batch or not.

For example, for a potion where you explode like a fireball when you drink it, it's a level three wizard spell so they already have the recipe. It takes six weeks for the alchemist to try to make a potion and costs a total of 3000 dinars and 3000 xp worth of bats and fire-themed monsters.

(You also get the xp from the monsters normally.)

These rules are from ACKS, page 117-118 for brewing potions and page 49-52 for hiring specialists.

Clarification: They can only make drinkable potions. Pōtāre is latin for drink.