Try Bach's Mass in B minor by John Eliot Gardner on the Archiv label.
This performance dates back to the 80s (1985, I think). Anyway, the mass
was performed on period instruments using A415 tuning. (It sounds like
Bb minor) Make sure to take time to listen to the Credo. Note: Once you
listen to a performance in the old baroque tuning, don't listen to the same
work in A440 or higher.
Jeremey