You might well be able to get it from the butcher or slaughterhouse, they'll still be around so long as people want to eat meat and meat is available. But since the 70s we've made insulin from yeast. If you can obtain the ingredients (that's the hard part here) and know what you're doing, that seems to me like it has got to be more scalable. But like I said, this is all idle speculation. The odds of asteroid impact anytime soon are slim.