Harvard Yearbooks
One possible data set that I identified early on was to do an survey of Harvard yearbooks over, say, a ten year period (1900-1910, for instance), and conduct a survey of clothing (if there are any photographs of students in evening dress) and/or tailoring advertisements.
The Harvard Yearbook of 1900 contributed some interesting fashion-related information. The one photograph of students in evening dress was of the debate club; it would be interesting to know why, or if that remains consistent in further years. There were also a good number of advertisements, many of which were from tailors, both in Boston and in New York City.
Unfortunately, later years had different photographs and no advertisements at all, so this source didn't end up being reliable as a source for a lot of data in a short period of time (see: Identifying the Data). However, they may be interesting to go back to at some point (even just for the tailoring advertisements from 1900), or to request earlier years.