The winter in Sfakia has been cold and wet this year, with snow higher up, so that might mean that some flowers will come out later than your visit. It's always worth going up to Anopoli for a variety of flowers along the village road or small paths. All the main gorges usually have interesting flowers in the spring, including the path (above the road) into the Ilingas gorge. The headland around Loutro, and the area above Livaniana also may have lovely displays of flowers early in the season.
I will be in Sfakia when you are there, so make yourself known to me (at the Lefka Ori) and we can talk about locations in more detail.