The only place you are likely to find any would be in the two main cities, Suva or Nandi. However, a lot of tourists don't spend much time there, and head out to the islands and coastal resorts.
Fijians very religious and tribal, so my uneducated guess is there won't be much of a gay culture with the locals.
Best bet would be to head out to one of the bigger party islands, especially during peak season. Some of the islands have multiple resorts with hundreds of people, with massive parties. Lots more western culture so odds are that would be a good place to start. almost 10 years ago