Hi, when i worked in the travel industry i use to recommend this website for surfing around the world. It is at least a start. As to where you can hire SUP's from perhaps ask these guys they might know.
www.globalsurfers.com/fiji.cfmI stayed on the Coral Coast you just have to remember that depending on where you are staying (I was at the Warwick) it was approx. 2 hours by taxi back to Nadi then you have to get out to the islands. There are some breaks around on the coral coast but the best ones are up off the islands off Nadi.
Good luck and enjoy.