Find the rom it's bundled with (Samfirmware/AndroidFirmwares.net/Samsung-Updates.com), download the rom, extract the modem.bin file, flash with Odin in phone section. Might be quicker than hoping who has the modem seeing your thread (understatement).
If it's important enough to cause you grief if it's lost, back it up. No excuses
Trolling for thanks is lame
Does Samsung's auto-brightness implementation crap drive you to self-harm ? A solution !
Failure to search is the leading cause of male impotence on XDA
If you don't know how to recover if things go wrong, what are you doing flashing custom roms ?