Stores seem to be pretty hit or miss with having green bananas out on their sales floor, but I'm pretty sure if you just inquired with a produce clerk at most places they could go in the back and grab you some. I know we usually had green ones in the back of the store where I worked in Aspen.
I did happen to find a place here that sells green bananas bagged up and they are super green, as you can see in the video. Those two in the bag are the last of a bunch of 10 and they are still that green. I do place them in the refrigerator though.
Most people that hear I'm eating green bananas cringe at the thought. To be sure, they are not like the ripe yellow ones. But in all honesty, they really are not bad. You just have to get in the mindset that you are not eating the type of sweet bananas you're accustomed to. Think of them as a different food altogether.
Anyway, green bananas are a little tricky to get open and I've found a good method that I'll share with you in the video below. Please note that it is not kid safe.