I don't know much about any saltwater fly fishing but there is a good article in the Summer 2006 Fly Tyer magazine titled Pops' Bonefish Bitters by David Klausmeyer. This article suggests that Belize's Turneffe Atoll is a fly-fishing dream destination. The Turneffe Flats Lodge is owned and operated by Craig Hayes. For more information you can contact them at 1-888-512-8812 or http://www.tflats.com
You might also checkout the current issue of the Saltwater Fly Fishing magazine. I believe it has an article over the area that you are going to be in as well.
Hope this helps.