There is a Fiji Expats Facebook page, this is probably a good place to start your hunt for new friends in Nadi and the surrounding areas (I have nothing to do with this page).
I wish I could say it's easy to meet friends in Nadi, but it isn't. A lot of people give up on Fiji because they find it hard to meet new people, but then one day everything just falls into place! So just give it some time!
Husbands/boyfriends, be warned! Married women not working or living in Denarau may find it even harder to make friends, the first couple of months are going to be tough.