What sort of 20's fashion?  I think that might help.  The issue I think is that most historical Poser clothing tends to be modeled on the iconic styles of the era.  The flapper and Coco Chanel's simplified lines being what became that icon for the 20's.

A hint as to whether you would like daywear, evening wear, high fashion, everyday stuff for the general population.  It is a decade when fashion went through a major upheaval, so some Edwardian pieces are still perfectly accurate since not everyone would want to be cutting edge.