I don't know if this will be helpful, but a few years ago I flew UA
in Y-class over Passover (this was when they still had meals on domestic flights). They had a fine-tasting, normal kosher meal, but it was not Kosher for Passover (it had many bread products). I don't know if that is specifically what you are interested in but you could try calling reservations and seeing if they can help you. If you're flying over passover, it would probably be worthwhile to take a little kosher food or matzah.