I need to use a hardware serial port (on a Mega) with GSM library

I need to modify the GSM library to use a hardware serial port, instead of the software serial driver. I had to patch the software serial code to interface to custom hardware (inverted rx data). I don't know where the GSM library driver source is located.

On a Macintosh it's something like:

/Applications/Arduino 1.0.5.app/Contents/Resources/Java/libraries/GSM