Noonsite is the place! Here's data on Mexico for example:
The only firearms allowed in Mexico are sporting guns which must have a valid Mexican hunting licence, obtained in advance. Other firearms must have a permit, and be declared to the authorities on arrival, who will keep them in custody until departure. The penalties for having an unauthorised gun on board are severe and can lead to seizure of the yacht and imprisonment of the captain.
10...you should search firearms here if you are not familiar with the major debate around carrying them while cruising. I choose to defend myself in other ways due to the inconvenience firearms bring to the cruiser rather than anything else. A nice automatic weapon would be a comfort in some places but the inter-country regs just make it too much of a pain for me.
No longer posting. Reach me by PM!