I think your best bet would be to simply try a local bar/dance club. I am more familiar with American Samoa where I worked on a two-month project; I took occasional weekend trips to Samoa (formerly Western Samoa). I didn't find any gay venues per se, but I did find that a number of local men at the clubs were not easily categorized as "gay" or "straight" but were just "friendly" so to speak.

There was a discussion here about a year ago on gay life in Tahiti. I think there are a lot of similarities, expect of course that Samoa is a lot less tourist-oriented.