It's a touchy subject I presume, because "proprietary" information like that could be used by competitors in any variety of ways, but in public filings I know of no airline nowadays that reports passengers separately by classes of service. Everybody flies coach in the eyes of DOT airline statistics.

There is, however, something called the Origin & Destination (O&D) Survey, which is based on a 10% sampling of the flight coupons collected by each of the reporting airlines. It contains a juicy load of information, including the origin and destination (duh) on the coupon, the ultimate destination (if connecting), the actual fare paid, etc., etc. But since this information is based on a subset of the actual traffic, it must be regarded with some caution. Nevertheless, it is the best way an airline can gauge how they are competing against other carriers on a particular route, without actually stealing their raw passenger data.