Music21 is a musicology software developed at MIT and includes within it a large corpus of western classical, and other, music.
From their website:
Music21 is a set of tools for helping scholars and other active listeners
answer questions about music quickly and simply. If you’ve ever asked yourself
a question like, “I wonder how often Bach does that” or “I wish I knew which
band was the first to use these chords in this order,” or “I’ll bet we’d know
more about Renaissance counterpoint (or Indian ragas or post-tonal pitch
structures or the form of minuets) if I could write a program to automatically
write more of them,” then music21 can help you with your work.
I have not examined their corpus, but their description indicates that it might have useful content for your effort.