You mean load-factors, and presumably by cabin, for specific flights? Not a chance.

Some DCAs such as the CAA in the UK publish historical data on passenger numbers and aircraft movements. With a little detective work and some insight this can give you load factors for some carrier-route combinations. But it's a bit-back-of-an-envelope, not day by day stuff and it's not cabin class specific.

For current/future flights, Expertflyer can give you some insight into demand through the way the airline is marketing the flight: but all that can be misleading and can change in the blink of an eye.