I have one, but I want to know what flower garden they are in because there are no white flowers you can walk in that I know of.
White Flabebe can be found in Red and Yellow Flower Beds in Route 4 and in Yellow and Purple Flower Beds in Route 7.
They can also be found in Normal Grass in Route 7 (Credit to fondant)
Source: Flabébé - Bulbapedia, Route 4 - Bulbapedia, Route 7 - Bulbapedia
Hope I helped :)
Where ever a flabebe is found, there is gonna be more of its colors.
So, if there is a flabebe in the grass/flower patch you just walked in, there is garenteed that there will be other colors of flebebe in that same patch.