There is a huge amount of material out there to find on these topics.
In Databases, search the fair title. Also alternatives. For example, the 1893 "Chicago World's Fair" is also called "The Columbian Exhibition."
On Google, try searching for the name of the fair, plus either "visual culture" or "artifacts" or "posters,:Suggested Search Terms" etc.
A search like this also provides good results: “world’s fairs and visual culture.”
If you find something written in the period you are studying, it may qualify as a primary source.
Vogue is perfect for historical research because it has every issue completely available going back to the late 1800s, including ads, articles, etc. All searchable by key word and date range. This amounts to PRIMARY sources. When off campus, login is required.
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