Mine go from March to July. What might be choice August bloomers in zone
8, if I may enquire?

R. diaprepes (and it's hybrid), Polar Bear can bloom that late, but for the
most part it is to the native species azaleas you look for really late blooming
- prunifolium, viscosum, maybe an auriculatum or two.
The humble R. ponticum can extend past the end of July in some places, but
usually peaks in June.