Haiti doesn’t have an army now. They had several military branches, and paramilitary groups too, up until 1995. Those groups were definitely armed. Where do you think the guns went when they were disbanded?
I don’t know where “here” is for you, but you can definitely buy AKs like that in most parts of the US.
Edit: actually I’m not sure what that rifle even is. It looks like an AK, but has an AR stock and it doesn’t look like an AK magazine… But the ejection port is only big enough for pistol rounds like 9mm. Given that, and the variety of guns in the other picture, I think they’re just getting whatever they can, wherever and whenever they can, so we’re not talking crates full of ARs coming over from the US very recently.