Hi Danie!
I've been there at the beggining of the year. As far as the period I went during the worse possible one (cyclon period) Unfortunately it came just when we arrived and was done by the time we left. Therefore I can not tell you a lot about diving. I've been able to dive cople of times on the east coast of Mauritius. There are couple of interesting wrecks, a very famous cave called "The Cathedral" (on the south-west coats if I remember well) plus the usual and beautiful coral reefs with their ecosystem. More info you can get from books like "Diving in Mauritius", I am sure you can find it on the net.
It is quite easy to travel from a part of the island to the other, normally using a rented car with a diver and they are not very expensive.
You can find good diving centers integrated with the hotels or resorts. They can offer all the stuff you may need. Top hotels have well equiped diving centers with reasonable quality gear available for renting. I would not advise you to try independent diving centers if they don't have a good recomandation, at least from the reception of the place were you are going to stay.
If you need more onfo make a post or mail me directly.
Victor