Please acknowledge that your situation is pretty unique. Just take a look at the comments: how many people say, or outright presume, that their company's code is already on GitHub? I'd wager that your org doesn't keep code at a 3rd party provider, right? Then, you're in a minority.

I don't mean to dismiss your concerns - in your situation, they are probably warranted - I just wanted to say that they are unique and not necessarily shared by people who don't share your circumstances.