Sources are always a challenge. However, if you know where to look, then you will be able to find tons of sources. In light of this let me, suggest several strategies.
First, go to the library and go to the databases of journals. You will be able to search by key terms. Type in toilet paper and history. You should get a few hits. Once you narrow down which articles you want to read, then get them and use these articles as the basis for further research, as you will have a nice bibliography. You might also want to search for other keywords, such as bathrooms, toilet bowls, and the like. Also keep in mind that the newest articles will have the most up to date bibliography.
Second, again you can do a search through key terms on your university's library website to see what books come up with the title of toilet paper. Once you get the book, you will have a huge bibliography to work through.
Let me start you off with one title:
Harkay, J. Russell (2006), "Roll Out: Toilet Paper Physics", Phenomenal Physics: A Guided Inquiry Approach.