If you are buying a small quantity of seed, you might be lucky and avoid any hassle. However, it takes a long time for the seeds to arrive, and most will not be viable when you try to get them to germinate. And it will take a lot of time to get flowers from plants grown from seeds. There are a lot of good nurseries in the North of the country that sell plants. Best thing when buying from a nursery is that you can get one plant with flowers at the price of 25 seeds you buy online, which may never germinate.
Some nurseries, try to get the numbers:
Pepiniere Renaissance( best one)
Pepiniere de Grand Baie
Pepiniere de Labourdonnais
Most hypermarkets like Super U, Jumbo, Lolo and others have stalls for seeds.