They have trade. Inside and outside.
Outside sure, but I don't think I have seen any internally. Do you have examples?
Currency facilitates trade. Next question: why do they need trade? (Besides cultural exports- let’s…. Not get into that.)
They can just replicate the other's civilization money if it is at a lower stage of technology advancement. In the scenario of the same or later technology stage, like the Ferengi Alliance, they would trade for technology, information and/or territories.
The one resource they have a desperate need is dilithium, which they had automated the extraction using the Doctor holograms lol.
Being shipped doesn't mean it is a trade deal, they offered assistance due to its strategic position as it is a disputed planet between the Federation and the Klingons. And if you're talking about the deal between the bartender and Cyrano Jones, he is independent from the Federation, like Quark's bar, any deal between would be external (and they seem to use credits as a currency?).
In a similar situation, Deep Space Station 9 is close to disputed territory and Federation candidate members. So again, they deal between Federation and others species. And the cargo ships in TNG aren't necessarily, doing any sort trade, they may simply hauling supplies for Federation planets and colonies.
Since they need it for every warp drive spaceship, I assume it would be a very well controlled resource. And due to its importance I don't think they would hire external help, so it would be fair to assume they use Federation miners and scientists to extract it. But again I don't think they mention any internal trade, so I assume they distribute it accordingly to each species or organization.