Henry, your best option to find one is on a website called ( gunbr0ker ) they're a site that allows private owners and small shops to sell their products so they usually have rare and hard to find firearms and accessories. I've already checked and they have several H&R ultra slug hunters in 20 gauge. Just Google gunbr0ker and type in the firearm you want and it'll pop up. Hope this helps.

Keep looking you will find it!

Henry, just click the first link here Sir : google.com/search?q=H%26R+ultra+slug+hunter+20ga&sxsrf=APq-WBvF4r9vPgnyg8bpnkVFJ-1_lQla1A%3A1645544786719&source=hp&ei=UgUVYvLbKOWlytMP1cGLyAo&iflsig=AHkkrS4AAAAAYhUTYhvh7GteF8GYngKJlnDVEFSPCgsn&ved=0ahUKEwjyzOKD1JP2AhXlknIEHdXgAqkQ4dUDCAg&uact=5&oq=H%26R+ultra+slug+hunter+20ga&gs_lcp=Cgdnd3Mtd2l6EAMyBAgAEA0yBggAEBYQHjoJCCMQJxBGEPsBOgQIIxAnOgoILhDHARDRAxBDOgQIABBDOhEILhCABBCxAxCDARDHARCjAjoQCC4QsQMQgwEQxwEQ0QMQQzoQCC4QsQMQgwEQxwEQowIQQzoOCC4QgAQQsQMQxwEQowI6CggAELEDEIMBEEM6CwgAEIAEELEDEIMBOgsIABCABBCxAxDJAzoFCAAQkgM6BQgAEIAEUABYgWlghG5oAHAAeACAAU6IAZELkgECMjaYAQCgAQE&sclient=gws-wiz

Do a Google search and you'll find a couple for sale along with other info about this model.