Well, my doubt was not based on lack of profit ...
I just cant really imagine how would that work.
You know, if you take Illithid mentality, it seems like litteraly any living creature (sometimes including other illithids) is for them either food, an incubator, or test subject ...
Now add psyonic powers so strong, so they can dominate mind of any sentient species by their meere presence ...
I just cant really imagine situation, when such creature would even bother to think about trade with anyone.

Then take who they have contact with:
- Deep Gnomes, that are usualy either enslaved or hiding to not be enslaved ...
- Duergars, who hate them with burning pasion, and are enslaving everything on sight ...
- Drows, who concider anyone to be lesser than themselves, and also are enslaving everything on sight ...
- And Myconids, who are most likely completely useless for them ...
Duno, maybe im missing something ...
But the way i see it, neither side have zero reason to try establish any friendly contact with ... well, basicaly any other group.

collected (magical) weapons
This is interesting theory ...
Question is: Where would they collect them from?

Surely Drow wouldnt surender their prisoners armed, just to buy their artefacts back.

And on the other hand, if Illithids would make their own raids for slaves/food ... they wouldnt need Drow supply.