Don't want to say this with certainty, but don't count on finding anything worth taking home. In Central America in general the only way to get a decent Cuatro (Ukulele even more difficult) is to have a local luthier build one. The quality there varies widely too, there is generally no humidity control, and you won't know for sure what you'll end up with if you do find someone and try to commission something.
Save your time for the mountains and beaches.