I bought this azalea from Honeycreek Nurseries. Their website doesn't list exactly WHICH azalea it is, though. It's simply labled "Azalea, White" (Rhododendron subgenus Azalea) Item #7182
There's also a more compact Southern Indica Azalea called 'Fielder's White' that has similar flowers but I'm not familiar with it. 'Mrs. G. G. Gerbing' gets really big so that might help some in the ID.