I have a commercially available handheld espresso machine that is no longer in production that has a similar design. I'm blanking on the name of it (edit: found it, the Mypressi Twist: https://coolhunting.com/food-drink/twist-espresso/), it kinda looks like a little black mallet - sphere at one end where you put the ground coffee and water, and the handle is where you insert nitrous canisters (whip cream chargers) for pressure. If I searched for a while on Home Barista I'm sure I could find it - it got great reviews there. You get 4 shots for each charger. It's really a fantastic little device!
To the original author of this post, I'd definitely recommend using whip cream chargers instead of CO2. They're usually cheaper, and you don't have to worry about the acidity concerns you bring up in your post.