If you want fly AF, use their web: http://gp.airfrance.fr/ (access password should be provided by airline you are working with) - it helps you with info about loads and with listing

KL - call KL office or check booking classes numbers - for example http://www.seatcounter.com/ - it doesn't tell you exact numbers, but if you see that no class is free, you should choose another flight

OS - call OS office for loads, for listing use www.flyzed.com

On both legs (CDG-VIE and VIE-AMS) are daily 5 flights or more, so I believe it will be not a problem to get on board one of these flights.

Michal,
CSA Czech Airlines
Prague