Your text has useful bibliographies inside of it! Use that information to search the Library catalog and the article databases.
I used your text's publisher and "dracula" in order to pull up any related books in Google Books. Try other search terms combined with "dracula" - like Mina, Van Helsing, etc.
"Welcome to my house! Enter freely and of your own will!" Count Dracula to Jonathan Harker, page 40 of your text.
I used your text's editor and the word "dracula" for this search in Google Scholar. Also, try the names of the critics and the word "dracula" and you may pull up other related articles that have been written by the critics you are studying, plus who else has read and cited the critics.