With much appreciation to the (no longer online) UC - Berkeley English Research Guide by Michaelyn Burnette.
AKA, perhaps someone has done some legwork for you! Use the MLA and library catalogs to see what already exists. Even if a source isn't entirely on target, always skim the bibliography.
Even some of our favorite resources, like the MLA, may apply headings a little inconsistently. Always note which field are available to you, and contrast and compare different methods, or try other keywords like "influence" or "transmission" or "translation".
Where is the best place for primary sources on your work? As always, the answer "it depends". In what time period was your work first published? Was it a book, song, movie, manifesto? Each database excels in a difference area.
Try the primary source listings by time period, and in particular the databases below. Experiment with quotation marks, alternative spellings, and plurals. Do not let any database give you the illusion it is complete.