I have an extra 5 gallon Adventures In Homebrewing (so new-ish, as in never used for soda) corny keg, in box, that I’m not likely to use any time soon. It’s clean and holds pressure well.
Asking $50 + shipping.
This thing weighs 12 lbs, but is 26”x9”x9” in the box, so recommended for buyers in New England/the northeast, primarily. Local pickup in Queens works also, if you prefer!