Is there any free source for current airline schedule data?
I am currently developing a plugin for virtual airlines to pull live data, and I use the FlightAware's API which is really good in my opinion. With a little bit of php magic you can get all the schedules for your airlines for free (if you sign up for the free account) or you can pay to get access to the getAirlineSchedule query which just basically does what it says.

https://uk.flightaware.com/commercial/flightxml/

There is the website if you're interested, to get access to the free area, sign up and click the 'get prices' area and the very left option should be the free pack ;)
If you're interested in my code which I am developing, you can check it out at my github;

https://github.com/RAZERZ/PullFlightData

Good luck ;)

EDIT: You get the data in the form of json, so you can pull strings of data from there :)