[quote=@Hunter of Dreams]
Would things such as arms dealers/black market rings/etc be plausible in this setting?
[/quote]

I don't see why not. But since there are technically no laws in no-mans-land, an illegal market would have to appeal to the wants of criminals within the established nations. There could be a black market within Arcadia, theoretically, but if there was, they'd have to be [i]very[/i] underground.

Alternatively, they could function outside Nation borders, and sell their product with mules that infiltrate places like Arcadia. Think something up and it's perfectly plausible.