I don't believe you can buy insurance like that here, but I do understand your concerns.
We just wound up a week of wedding activities - including outdoor ceremony and reception. 7 days before the wedding it was horrible weather, on wedding day it was perfect (whew).

A few suggestions that should make you a bit more relaxed --- first, hire a wedding planner and communicate often with them. Make an excellent plan well in advance. Then play devil's advocate and think of the major things that could derail the event, and at least know what would be a reasonable back-up plan.
As with anything, the more people, the more that can go wrong - and the more elaborate the event the more that can go wrong --- the best insurance of all is to keep it simple. Our family could not manage the "simple" part so we hired Iraida and prayed a lot.
Family of Bride and Groom stayed at Caye Villas, and we used the gardens/grounds for the wedding and reception. It was stunning. It also gave a private central gathering spot for everybody during the week of arrivals and preparation.