I've read (on multiple occasions) that Bach used already-existing chants and melodies as a basis for his own works (harmonisations, motets, cantatas...). Not just him, but almost every other composer before Bach used more or less the same method for composing. Also, many cantus firmi (used in masses, motets) were drawn from the gregorian chants.
That's what I read. I wanted to write a short chorale myself (as a part of a bigger work), and off I went to search for those tunes/chants/melodies. Guess what! I found 0. Nothing. Searched for chants, plainsong, gregorian this and that, and not a single staff of music out there on the web(apart from the four line staff and neumes, which i can't read)
Is there any resource for that kind of stuff (chants, plainsongs, church melodies...) that you are aware of, and if yes, please let me know.