Don't know of where to get a lefty 760 but I can help with the safety. I don't think Remington made a left handed 760.

Pull out the trigger group. Once you pull it out you can see a roll pin just above the safety selector switch. That roll pin is holding in a spring and detent plunger. Drive out that roll pin but make sure that you don't let the spring go flying. Turn the trigger group upside down and tap out the spring and plunger then you can turn around the safety selector switch and reinstall the plunger, spring and the roll pin.