Determining how full a flight was
 

I'd like to find out how full a specific flight was - my particular query is for an American Airlines flight this past spring. Is there an online way to do this? If not, is there another procedure?

Ive checked FlightStats.com and FlightAware.com, but no joy there.

Thanks for any tips

short answer: No.
Govt published transtats are the closest you'll get however they won't tell you an individual flight, that info is proprietary.