Use of poems, etc. in papers is scattered. Some Scottish and English journals, as well as some in the U.S. and Canada also used them as filler, or accepted a few papers (very few) on specific material but the practice was never regularized, except in some of the literary journals.
Folk material was uncommonly used, since it was considered illiterate or of poor quality- and very few song-catchers were out there before the 20th C.

The practice depended upon editors and ownership policy, so some papers and journals never used them.

That is why a search is tedious and time-consuming, and possibly costly. Now that some journals and papers have been digitized, the searches are more easily done. Many, however, require a subscription.

I don't have the time or money to subscribe (except to Journal of American Folklore, which started in the 1880s and has articles on folk material from all over). The articles, of course, are mostly on UK and American and Canadian material, as would be expected.