If you have an opportunity, try to find these articles (though not easy-to-read ones in scholarly journals) at local or college libraries:

Paul Franklin Baum, "The English Ballad of Judas Iscariot." PMLA [Publications of the Modern Language Association], vol. 31 (1916), pp. 181-189.
Paul Franklin Baum, "The Mediaeval Legend of Judas Iscariot." PMLA, vol. 31 (1916), pp. 481-632. [very comprehensive article]
Donald G. Schuler, "The Middle English Judas: An Interpretation." PMLA, vol. 91 (1976), pp. 840-844.
Mary-Ann Stouck, "A Reading of the Middle English Judas." Journal of English and Germanic Philology, vol. 80 (1981), pp. 188-198.

I remember reading parts of them some twenty years ago, but have forgotten the contents. The manuscript (with transcription and translation) of "Judas" is online (Click here).

~Masato