I couldn't find anything of significance for fly fishing in Bali when I researched for my honeymoon. Asking at the concierge of the resort served me no better. The reefs are all completely fished out, so there's minimal DIY from what I understand as well. I did one half day of conventional fishing for giant trevally, but no success. From what I understand, you need to do a full day to have enough time to get to the good areas for GTs - but I was lucky enough the wife was willing to do a half day on our honeymoon, so I didn't push it!