I wish you luck in your search. The magazine sold out of all Hastings high-rib barrels and parts in what seemed like seconds after the closure of Hastings was announced. I have a barrel and both choke tubes they offered and have turned down as much as twice what they cost new. From the amount of people who say they can't find chokes for them, I'm assuming that no company makes chokes to fit those barrels. They are flush-fit tubes that are as long as most extended tubes.
Above is a photo of a Hastings tube for the high-rib barrel and a RemChoke tube that compares their lengths.