Plantation island fiji...has a bit ,not flash but will get you going .
cook islands .captain Tamas .they have a site .

I stayed at Shangri-La 10 years ago and wouldn't recommend it for windsurfing at all. Hopefully things have changed but I would be surprised.

I was told very similar things to the point that I had thought it definitely not worth lugging my own gear for 4 days (there for a wedding - superb venue for that). What I found was 90's learners gear (old long board) and was told by the staff that I was really good as they hadn't seen anyone sail it successfully for some time. It was offshore wind every day so very difficult if you are a beginner. I only went out so I could say I've windsurfed in Fiji.

Other parts of Fiji or Raro better. Have you looked at New Caledonia - I believe windsurfing is pretty big there from the event reports and there is a shop...