Chances are that if you can't find it here you don't really need it anyway. The point of being here in Belize/Ambergris Caye is not eating and drinking and doing everything you did back in the US or Canada.
In terms of diving, fishing, snorkeling, water sports they also get cheaper when you live here as you will most likely develop relationships with people who operate these types of business's.
I (my wife and I) have been here for about 10 years now and moved here from Austin Texas. Our cost of living is about the same as it was there. We spend the money on different things ex: we spend more on food and wine but less on going out, cars, insurance, travel, etc.
The moral of this story is that if you want to have the Maitre D'hotel bring you a demi bottle of 1969 domaine de Cheval Blanc to drink with your kobe beef carpaccio you are in the wrong place. If you want to dive on the second largest barrier reef in the morning and then have a plate of rice and beans with stewed chicken from a food stand on back street for $8 BZD paired with a belikin then you have come to the right place!