Is this question about practicing modesty, or about the existence of traditional Catholic fashion designers?
With regard to the latter:
My first guess was yes, there probably are some traditional Catholic fashion designers out there. Because there are plenty of traditional Catholic designers of other things (e.g. photographers, graphic designers, web designers, layout, video, etc.), so why not fashion?
But on second thought, I can certainly see why there may be an absence of traditional Catholics among the fashion industry: fashion isn't something that trad men are particularly drawn to. So very few (if any) trad men would pursue fashion as a career. And as for the trad women, they generally get married and raise children rather than pursuing a career.