Sally carries 40. They also carry 50, but you need a beautician license to purchase it because it's powerful enough to kill a bitch.
The Food Grade peroxide is probably fine. Peroxide is edible, AFAIK, in small doses, lol. It's in teeth whitening toothpaste and shit,so it can at least go in your mouth for a little.
I don't recommend trying it though.
the 20 vol. is weaksauce. You may have to leave it out longer. If you're leaving it out in the sunlight, a few hours should do it.