The gunrunners could do their business subtly and the government to not sanction their actions, while also not cracking down on them (too much).
The Prez can deal with the gunrunners in a reasonable way but still beat the ass of slavers and drug dealers. It would be best, though, if he and the Akori government act totally clueless about the whole gunrunning thing.
Akori won't be the only port for gunrunners. The whole CONTINENT will be rife with people sending arms to help the noble causes of various revolutionaries in whatever part is being dicked over by neocolonialistic cockery.
Gunrunners, drugrunners, slavers, all of this will be a natural consequence of all the unwanted attention the continent is getting.
Either way, you COULD send your Serenity guys over there as a token gesture to "stop anarchistic" or "lawless" or whatever influences from taking hold. But in REALITY, you'd actually be expanding your sphere of influence in ANOTHER bid at neocolonial dickery - for your own profit.
And THEN you'd allow the gunrunners to sell guns to revolutionaries at the West side of the continent, while also selling your own guns and stuff to people!
(If you're in the MESS, this would be a plus for whatever MESS intervention is going on at Valeria. You'd join the Canissians and Cascadians in trying to dick the Shepistanis and Japanistanis over)

@ Karmic and PeZook:
The FUN will be an economic alliance, then. For money, for trade, for profit and for richness!
There WILL be under-the-table military defense deals and contracts for missiles and shit. I mean, if one of our more profitable and beneficial buddies gets attacked, we'd have to DEFEND OUR INVESTMENTS!
But there won't be obligations. Just... protection of interests.

Shroomania probably has an already-existing (or de facto) open borders agreement with both PeZookia and Canissia, owing to our awesomely friendly relations. It'd be like Canadia and the USA or something.
The Shroomanian Commonwealth would be a more... uhh... symbolic thinggy. Sort of like how Australia and Canadia and stuff are Commonwealth nations, but don't really owe Britain anything aside from having Queen Elizabeth on their monies or something.