Since there is no guide service, this group asked if they could bring their own equipment and hire a fishing boat to take them. I want to give them the most accurate information available so I did a little more research into the restrictions and CONAPESCA states "Underwater fishing is limited to five fish per day, using rubber band or spring type harpoons, and only while skindiving." Link. It looks like they just need a fishing license. I'll let you folks know how it goes if they end up pursing it.

Thanks for looking that up and refreshing my memory.

You might contact one of the local diving outfits as well as a local fishing charter service for helpful details. The diving folks can tell you where you definitely should NOT spearfish since there are a few ecologically sensitive areas, and the fishermen can help you with the license and take you to where the better spots are.