Here are the samples of the "circus" inspired ephemera I found with your custom journal in mind. These are two original vintage french programs that I found at an Antique Book Market in Paris.
Below: Deep burgundy and purple colors
This program is in slightly better condition than the following one.
Although, they would both work well as covers.
Dimensions: width: 5 1/2", height: 8 3/8"
Program Year : 1951
Below: Bright yellow and reds.
Program Year: 1952